SUBLEASE AGREEMENT

Exhibit 10.23

SUBLEASE AGREEMENT

     This Sublease Agreement (this “Sublease”) is made as of the 25 ^th day of June, 2008 (the “Effective Date”) between DIECA COMMUNICATIONS INC., a Virginia corporation (“Tenant”), and K12 INC., a Delaware corporation (“Subtenant”).

R E C I T A L S :

     A. By a certain Deed of Lease dated July 8, 2002, made between TST Woodland Funding I, L.L.C. (“Original Landlord”), and Tenant, as amended pursuant to the First Amendment To Deed of Lease (the “First Amendment”) dated March 31, 2005 by ACP/300 Corporate Park Drive, LLC, a Delaware limited liability company, successor in interest to Original Landlord (the “Master Landlord”) and Tenant (collectively, the “Master Lease”), a copy of which is attached hereto as Exhibit A, the Master Landlord leased to Tenant a portion of the property located at 2300 Corporate Park Drive in Herndon, Virginia (the “Master Premises”).

     B. Tenant desires to sublet to Subtenant and Subtenant desires to sublet from Tenant a portion of the Master Premises. Specifically, Subtenant desires to sublet from Tenant approximately 6,192 rentable square feet on the fourth (4 ^th ) floor of the building (the “Subleased Premises”), a copy of the floor plan detailing the Subleased Premises is attached hereto as Exhibit B, per the terms and conditions contained herein. Such Premises shall not be remeasured by Tenant during the Term, and if remeasured by Master Landlord, in no event shall Subtenant’s costs associated with the rentable square footage increase or decrease.

          NOW, THEREFORE, in consideration of the mutual agreements herein contained, and for other valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto agree as follows:

A G R E E M E N T :

1. MASTER LEASE

     A. Tenant represents and warrants to Subtenant that attached hereto as Exhibit A is a true, correct and complete copy of the Master Lease and all amendments thereto.

     B. Unless otherwise defined herein, all capitalized terms shall have the defined meanings ascribed to them in the Master Lease.

     C. Except as set forth below and except as otherwise provided in this Sublease, the terms and conditions of this Sublease shall include all of the terms of the Master Lease and such terms are incorporated into this Sublease as if fully set forth herein, except to the extent they are inapplicable to, inconsistent with, or modified by the

terms of this Sublease and except that: (i) each reference in such incorporated sections to “Lease” shall be deemed a reference to this “Sublease”; (ii) each reference to “Landlord” and “Tenant” shall be deemed a reference to “Tenant” and “Subtenant”, respectively, except as otherwise expressly set forth herein; (iii) with respect to work, services, utilities, electricity, repairs (or damage caused by Master Landlord), restoration, insurance, indemnities, reimbursements, representations, warranties or the performance of any other obligation of Master Landlord under the Master Lease, whether or not incorporated herein, the sole obligation of Tenant shall be to request the same in writing from Master Landlord as and when requested to do so by Subtenant, and to use Tenant’s commercially reasonable efforts (which shall not include the institution of legal proceedings by Tenant, but which may include allowing Subtenant, at Subtenant’s sole cost and expense, to institute legal proceedings in Tenant’s name (if necessary), by attorneys approved by Tenant, which approval shall not be unreasonably withheld, conditioned or delayed) to obtain Master Landlord’s performance; (iv) with respect to any obligation of Tenant to be performed under this Sublease, wherever the Master Lease grants to “Tenant” a specified number of days to perform its obligations under the Master Lease, except as otherwise provided herein, Subtenant shall have three (3) fewer days to perform the obligation, including, without limitation, curing any defaults; (v) with respect to any approval required to be obtained from the “Landlord” under the Master Lease, such approval must be obtained from both Master Landlord and Tenant, and Tenant’s withholding of approval shall in all events be deemed reasonable if for any reason Master Landlord’s approval is not obtained; (vi) in any case where the “Landlord” reserves or is granted the right to manage, supervise, control, repair, alter, regulate the use of, enter or use the Subleased Premises or any areas beneath, above or adjacent thereto, such reservation or grant of right of entry shall be deemed to be for the benefit of both Master Landlord and Tenant; (vii) in any case where “Tenant” is to indemnify, release or waive claims against “Landlord”, such indemnity, release or waiver shall be deemed to run from Subtenant to both Master Landlord and Tenant; and (viii) in any case where “Tenant” is to execute and deliver certain documents or notices to “Landlord”, such obligation shall be deemed to run from Subtenant to both Master Landlord and Tenant.

     D. This Sublease is and at all times shall be subject and subordinate to the Master Lease and the rights of Master Landlord thereunder. Subtenant hereby expressly assumes and agrees for the benefit of the Master Landlord: (i) to comply with all provisions of the Master Lease which are assumed by Subtenant hereunder; and (ii) to perform all the obligations on the part of the “Tenant” to be performed under the terms of the Master Lease with respect to the Subleased Premises during the term of this Sublease. In the event the Master Lease is terminated or cancelled for any reason whatsoever, this Sublease shall terminate simultaneously with such termination or cancellation and, unless it is determined in a final, non-appealable judgment that such termination is a result of Tenant’s default under the Master Lease, or Tenant’s gross negligence or willful misconduct, without any liability of Tenant to Subtenant. In the event of a conflict between the provisions of this Sublease and the Master Lease, as between Tenant and Subtenant, the provisions of this Sublease shall control.

     E. The parties acknowledge and agreement that notwithstanding anything to the contrary in this Sublease or the Master Lease, Section 18 of the First Amendment shall not apply and have no force nor effect with regard to the Subtenant.

2. WARRANTY BY LESSOR

Tenant warrants and represents to Subtenant that the Master Lease is in full force and effect, has not been amended or modified except as expressly set forth herein, that all obligations of Tenant have been satisfied, that Tenant is not now, and as of the commencement of the Term hereof will not be, in default or breach of any of the provisions of the Master Lease, nor to the best of Tenant’s knowledge is there any event with which the giving of notice or the passage of time or both would become a default or breach under the Master Lease and that Tenant has no knowledge of any claim by Master Landlord that Tenant is in default or breach of any of the provisions of the Master Lease. Tenant has not received written notice of any violation or alleged violation of law, including but not limited to the Americans with Disabilities Act of 1990, as may be amended (“ADA”) with respect to the Subleased Premises. Tenant, as of the Effective Date, has not received written notice of any mechanic’s liens charged against the Premises. During the Term of this Sublease, the Tenant agrees not to amend or modify the Master Lease in such a manner as to increase Subtenant’s obligations under this Sublease or adversely impact Subtenant’s rights under this Sublease without prior written notice to and reasonable approval by Subtenant. During the Term of this Sublease, Tenant shall not voluntarily terminate the Master Lease with respect to the Subleased Premises, nor will Tenant knowingly act or knowingly fail to act in such a manner as to cause the termination of the Master Lease. Should Tenant receive written notice from Master Landlord regarding any default or other material issue under the Master Lease or notices of any violations, mechanic’s liens or any other notices affecting the Subleased Premises, Tenant shall provide a copy such notice(s) to Subtenant within two (2) business days of Tenant’s receipt of said notice(s).

3. SUBLEASED PREMISES

Tenant hereby subleases to Subtenant on the terms and conditions set forth in this Sublease the Subleased Premises. Subtenant accepts the Subleased Premises in their present “As-Is” condition and shall be responsible, at its cost and expense, for all alterations, improvements, additions and other work desired for its use and occupancy of the Subleased Premises, except as specifically stated in this Sublease. For the avoidance of doubt, Tenant shall have no obligation whatsoever to make or pay the cost of any alterations, improvements or repairs to the Subleased Premises, including, without limitation, any improvement or repair required to comply with any law, regulation, building code or ordinance (including the ADA). In addition, Tenant shall have no obligation to perform any repairs or any other obligation of Master Landlord required to be performed by Master Landlord under the terms of the Master Lease and Subtenant shall look solely to Master Landlord for performance of said obligations. Tenant shall, however, request performance of the same in writing from Master Landlord promptly

after being requested to do so by Subtenant, and shall use Tenant’s commercially reasonable efforts (which shall not include the institution of legal proceedings by Tenant, but which may include allowing Subtenant, at Subtenant’s sole cost and expense, to institute legal proceedings in Tenant’s name (if necessary), by attorneys approved by Tenant, which approval shall not be unreasonably withheld, conditioned or delayed) to obtain Master Landlord’s performance. Tenant hereby assigns to Subtenant, for so long as this Sublease shall be in force and effect, any and all rights of Tenant under the Master Lease with respect to the Subleased Premises and causes of action which Tenant may have against Master Landlord with respect to the Subleased Premises due to default by Master Landlord under the Master Lease.

4. TERM

The term of this Sublease shall commence on the later of: (a) July 1, 2008; and (b) the date that Master Landlord consents to this Sublease or possession of the Subleased Premises is delivered to Subtenant (“Commencement Date”), and end on July 31, 2010 (“Termination Date”), unless otherwise sooner terminated in accordance with the provisions of this Sublease. In the event the Term commences on a date other than the Commencement Date, Tenant and Subtenant shall execute a memorandum setting forth the actual date of commencement of the term. Possession of the Subleased Premises shall be delivered to Subtenant on the Commencement Date; provided, however, once the Master Landlord consents to this Sublease, Subtenant shall be permitted access to the Subleased Premises within five (5) business days of such consent in order for Subtenant to complete (through Subtenant’s contractor or vendor or by Subtenant’s employees or other agents) the cabling of telephone, computer, security systems, office equipment and the like; provided that Tenant shall not be required to provide Subtenant with such access unless Subtenant has demonstrated its compliance with the insurance requirements provided in Section 13 of this Sublease. Notwithstanding anything to the contrary in this Sublease, if Tenant fails, for any reason other than the acts or omissions of either Subtenant or the Master Landlord (including without limitation the Master Landlord’s failure to timely consent to this Sublease) or the agents or employees of Subtenant or Master Landlord, to provide possession of the Subleased Premises on the Commencement Date, the date the Rent (as defined below) commences will be extended for each day of delay beyond such date and provided further that if Tenant fails to provide possession of the Subleased Premises on or before August 1, 2008 (subject to the exceptions set forth above), then Subtenant shall have the right to terminate this Sublease by written notice delivered to Tenant on or before August 15, 2008, upon which the parties shall have no further obligations to each other under this Sublease.

5. RENT

Subtenant does hereby agree, without notice, deduction or offset, to pay to Tenant, as the monthly rent for the Subleased Premises (“Rent”), the following amounts for the term of the Sublease:

Rent includes all Operating Expenses and Taxes contemplated under the Master Lease and Tenant hereby acknowledges and agrees that Subtenant shall not be responsible for any other costs not specifically and expressly provided for herein, including but not limited to costs or charges for Building or common area maintenance, utilities or taxes. However, except as otherwise expressly provided in this Sublease, Subtenant shall pay any other additional costs or expenses incurred under the Master Lease related to the Sublease Premises or Subtenant’s occupancy thereof (including, without limitation, the cost of all overtime HVAC, energy and other services costs provided to Subtenant and/or the Sublease Premises and not included in Operating Expenses or Taxes). Unless such costs and expenses can be paid directly to Master Landlord, Subtenant shall reimburse Tenant for such other amounts within ten (10) business days of receipt of an invoice (attaching the charges of the Master Landlord) from Tenant therefor. For the purposes of this Sublease and all of Subtenant’s obligations hereunder, Rent and any other sums due to Tenant from Subtenant under this Sublease shall together constitute “Rent.”

All payments of Rent due under this Sublease shall be paid in advance at least three (3) business days prior to when the corresponding payments are due and payable under the Master Lease. Said payment shall be made to Tenant, and shall be mailed to the address of Tenant or any other address which Tenant may in writing designate. The first month’s rent payment in the amount of $14,964.00 shall be due and payable by Subtenant to Tenant upon Subtenant’s execution of this Sublease.

6. USE OF PREMISES; ACCESS

Notwithstanding anything contrary to the Master Lease, the Subleased Premises shall be used and occupied only for general office purposes in accordance with the applicable zoning regulations and for no other use or purpose. Subtenant shall not use, store or dispose of, in or from the Subleased Premises, any substances, materials, chemicals or gases which are defined and regulated as being hazardous or toxic under applicable federal, state or local laws and regulations except for such substances, materials, chemicals or gases in small amounts as used in the ordinary course of the operation of Subtenant’s business which use shall at all times be in strict adherence to and compliance with all applicable environmental laws and the terms of the Master Lease. Subject to the terms and conditions of the Master Lease, Subtenant shall have access to the Subleased Premises twenty-four (24) hours per each day of the year. Tenant shall provide fifty (50) of its electronic access cards for the Subleased Premises and shall, at its sole cost and expense, cause the Master Landlord to reprogram the electric access system such that only the foregoing 50 cards shall provide access to the Subleased Premises (except with respect to the Master Landlord and Tenant as permitted and limited by this Sublease), and pay the costs associated with obtaining such cards if such cards provide access to the Master Premises in excess of the Subleased Premises.

7. AGENCY DISCLOSURE

Subtenant and Tenant each warrant that they have dealt with no other real estate broker(s), finder(s), or other person(s) in connection with this transaction other than The Staubach Company – Northeast, Inc., as Subtenant’s broker, and CresaPartners, as Tenant’s agent, both of which shall be compensated by Tenant pursuant to a separate agreement. Tenant and Subtenant each shall indemnify and hold the other harmless from any breach by it of this representation.

8. ATTORNEYS’ FEES

If Tenant or Subtenant shall commence an action against the other arising out of or in connection with this Sublease, the prevailing party shall be entitled to recover its costs of suit and reasonable attorneys’ fees.

9. FURNITURE

Subtenant shall have the right to utilize certain of the existing workstations and furniture within the Subleased Premises through the term of the Sublease at no cost to the Subtenant (excluding certain personal property of the Tenant). The Master Landlord owns the furniture and workstations and therefore Tenant and Subtenant have no rights to the furniture after the expiration of the Sublease term. Attached as Exhibit C is a list of the items of furniture within the Subleased Premises that Subtenant will retain (the “Sublease Furniture”). Any items of furniture that had been in the Subleased Premises but are not listed on Exhibit C as Sublease Furniture shall have been removed by Tenant, at its sole cost and expense, from the Subleased Premises prior to the Commencement Date. Subtenant shall have no further obligation to Tenant or Master Landlord regarding such items of furniture.

10. NOTICES

All notices and demands which may or are to be required or permitted to be given by either party on the other hereunder shall be in writing. All notices and demands by the Tenant to Subtenant shall be sent by United States Mail, postage prepaid, or by nationally recognized overnight carrier addressed to the Subtenant at the Subleased Premises, and to the address hereinbelow, or to such other place as Subtenant may from time to time designate in a notice to the Tenant. All notices and demands by the Subtenant to Tenant shall be sent by United States Mail, postage prepaid, or by recognized overnight carrier addressed to the Tenant at the address set forth herein, and to such other person or place as the Tenant may from time to time designate in a notice to the Subtenant.

11. REMOVAL OF ALTERATIONS

Notwithstanding anything in the Master Lease or this Sublease to the contrary, Subtenant shall not be required at the termination of the Sublease to remove alterations, fixtures, equipment and other property at the Subleased Premises unless such items or alterations are installed by or at the request of Subtenant. Unless the Master Landlord does not require such restoration or removal, Subtenant shall be solely responsible for the restoration of any items or alterations that are removed by or at the request of Subtenant and/or the removal of any items or alterations that are installed by or at the request of Subtenant.

12. CONSENTS

Each of the signatories set forth below represents and warrants that it is duly authorized to execute and deliver this Sublease, to bind the person for which such signatory signs and that such person has obtained all consents and approvals necessary to execute and deliver this Sublease. Additionally, except for the consent of the Master Landlord, each party represents and warrants to each of the other parties that it has obtained all consents and approvals necessary to execute and deliver this Sublease.

13. INSURANCE

     A. Subtenant agrees that Subtenant will, at all times during the Term of this Sublease, maintain and pay for such insurance as is required under the Master Lease, naming the Master Landlord and Tenant as “additional insureds” under the policy or policies carried by Subtenant. The Subtenant further covenants that in the event that the insurance policy evidenced in the certificate is canceled or materially amended it will advise the Tenant in writing to this effect forthwith. In the event that Subtenant fails to maintain the insurance required by this Section, then the Tenant shall have the right to obtain such insurance on behalf of Subtenant. In the event that Tenant obtains such insurance on behalf of Subtenant, then Subtenant shall reimburse Tenant for the cost thereof within five (5) business days of Tenant’s demand for reimbursement.

     B. Tenant and Subtenant each hereby releases all causes of action and rights of recovery against each other and their respective agents, officers and employees for any loss, regardless of cause or origin, to the extent of any recovery to either party from any policy(s) of insurance carried or required to be carried hereunder. Tenant and Subtenant agree that any policies presently existing or obtained on or after the date hereof (including

renewals of present policies) shall include a clause or endorsement to the effect that any such release shall not adversely affect or impair said policies or prejudice the right of the releasor to recover thereunder.

14. PARKING

Subtenant shall be entitled to use parking spaces in accordance with the terms of the Master Lease, including but not limited to Section 13 of the First Amendment concerning reserved parking spaces of which Subtenant shall be entitled to its proportionate share based on the ratio of Subleased Premises to Master Premises.

15. SIGNAGE

Subtenant shall have the rights to suite entry signage and building directory signage pursuant to the terms contained in the Master Lease.

16. CONDEMNATION

In the event of damage or destruction of the Subleased Premises or the taking of all or any part thereof under the power of eminent domain, this Sublease shall terminate only if the Master Lease is terminated as a result thereof.

17. EMERGENCY POWER SYSTEM

     Subject to the terms and conditions of the Master Lease, Subtenant shall have the right, with Master Landlord’s consent pursuant to the Master Lease, to connect certain equipment into the Master Landlord’s emergency power generator and uninterrupted power supply systems (“Emergency Power System”). Subtenant shall pay directly to the Master Landlord all costs and expenses related to the Subtenant’s actual usage of the Emergency Power System. In the event that Subtenant is not permitted to pay such costs directly, then Tenant shall pay the costs and expenses of the Emergency Power System and the Subtenant shall promptly reimburse the Tenant for Tenant’s actual costs incurred with respect to the Subleased Premises; provided that Tenant submits reasonable supporting documentation regarding such costs.

18. DEFAULT

Subtenant shall be in material default of its obligations under this Sublease if any of the following events occur:

          A. Subtenant fails to pay any Rent within five (5) business days after receipt of written notice from Tenant that such item of Rent is due and unpaid; or

          B. Subtenant fails to perform any term, covenant or condition of this Sublease (except those requiring payment of Rent) and fails to cure such breach within

thirty (30) days after delivery of a written notice to Subtenant specifying the nature of the breach; provided, however, that if more than thirty (30) days are reasonably required to remedy the failure, then Subtenant shall not be in default if Subtenant commences the cure within the thirty (30) day period and thereafter diligently completes the cure; or

          C. Subtenant makes a general assignment of its assets for the benefit of its creditors, including attachment of, execution on, or the appointment of a custodian or receiver with respect to a substantial part of Subtenant’s property or any property essential to the conduct of its business; or

          D. Subtenant abandons (without payment of Rent) the Subleased Premises in violation of the Master Lease; or

          E. Subtenant commits any other act or omission which constitutes a default under the Master Lease, which has not been cured after delivery of any written notice required and passage of three-quarters ( ³ / 4 ) of any applicable grace period provided in the Master Lease as modified, if at all, by the provisions of this Sublease.

19. SECURITY DEPOSIT

Subtenant shall provide Tenant prior to the execution of this Sublease a security deposit in the amount of $14,964.00. Tenant may use the security deposit, or any part of the deposit, to satisfy any default of Subtenant and any expenses arising from such default. If any portion of the security deposit is so used or applied, Subtenant shall, within five (5) business days after written demand therefore, deposit cash with Tenant in an amount sufficient to restore the security deposit to its original amount. Tenant may commingle the security deposit with its own funds and Subtenant shall not be entitled to interest on the security deposit. Any remaining balance of the Security Deposit shall be returned to Subtenant at such time after the Termination Date that all of Subtenant’s obligations under this Sublease have been fulfilled, but in no event later than thirty (30) days following the Termination Date.

20. ASSIGNMENT AND SUBLETTING

Subtenant’s rights to assign, transfer or hypothecate the leasehold estate under this Sublease, or any interest therein shall be governed by the Master Landlord pursuant to Article 13 of the Master Lease and by the Tenant pursuant to such Article 13 as incorporated into this Sublease.

21. ENTIRE AGREEMENT; AMENDMENTS

This Sublease contains all agreements between the parties with respect to any matter mentioned herein, and no other prior or contemporaneous agreement or understanding shall be effective. This Sublease may not be amended except by the written agreement of all parties hereto.

22. WAIVER

If either Tenant or Subtenant waives the performance of any term, covenant or condition contained in this Sublease, such waiver shall not be deemed to be a waiver of any subsequent breach of the same or any other term, covenant or condition contained herein, or constitute a course of dealing contrary to the expressed terms of this Sublease. The acceptance of Rent by Tenant shall not constitute a waiver of any preceding breach by Subtenant of any term, covenant or condition of this Sublease regardless of Tenant’s knowledge of such preceding breach at the time Tenant accepted such Rent. Failure by Tenant to enforce any of the terms, covenants or conditions of the Sublease for any length of time shall not be deemed to waive or decrease the right of Tenant to insist thereafter upon strict performance by Subtenant. Waiver by Tenant of any term, covenant or condition contained in this Sublease may only be made by a written document signed by Tenant, based upon full knowledge of the circumstances.

23. RELATIONSHIP OF PARTIES

This Sublease does not and shall not create the relationship of principal and agent, or of partnership, or of joint venture, or of any other association between Tenant and Subtenant, except that of sublandlord and subtenant.

24. NO DRAFTING PRESUMPTION

The parties acknowledge that this Sublease has been agreed to by both the parties, that both Tenant and Subtenant have consulted with attorneys with respect to the terms of this Sublease and that no presumption shall be created against Tenant because Tenant drafted this Sublease.

25. COUNTERPARTS

This Sublease may be executed in one or more counterparts, each of which shall be deemed an original, and all of which together shall constitute one and the same instrument.

26. MASTER LANDLORD’S CONSENT

     After its execution by Tenant and Subtenant, this Sublease shall be effective only upon obtaining the written consent of Master Landlord, or its duly authorized agent. Promptly after the execution of this Sublease by the Tenant and Subtenant, Tenant shall use its commercially reasonable efforts to secure the Master Landlord’s consent to this Sublease and shall keep Subtenant reasonably apprised of the status of such efforts.

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THIS SUBLEASE SHALL BE OF NO FORCE OR EFFECT UNLESS CONSENTED TO BY MASTER LANDLORD WITHIN 30 DAYS AFTER EXECUTION HEREOF, IF SUCH CONSENT IS REQUIRED UNDER THE TERMS OF THE MASTER LEASE.

Exhibit A

Master Lease

Exhibit B

Subleased Premises