UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q/A

Amendment No. 2

(Mark One)

For the quarterly period ended September 30, 2011

OR

For the transition period from              to             

Commission File Number: 001-33883

K12 Inc.

(Exact name of registrant as specified in its charter)

(703) 483-7000

(Registrant’s telephone number, including area code)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports) and (2) has been subject to such filing requirements for the past 90 days.    Yes  þ        No  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§ 232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  þ        No  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).    Yes  ¨        No  þ

As of November 7, 2011 the Registrant had 36,364,429 shares of Common Stock, $0.0001 par value outstanding.

Explanatory Note

The Securities and Exchange Commission has adopted rules requiring companies to provide financial statement information in XBRL (eXtensible Business Reporting Language). This Amendment No. 2 to our quarterly report on Form 10-Q for the quarterly period ended September 30, 2011 (the “10-Q Report”) is being filed solely to furnish Exhibit 101 XBRL interactive data files in accordance with Rule 405(a)(2) of Regulation S-T. This amendment does not otherwise change or update the disclosures set forth in the 10-Q Report as originally filed on November 14, 2011 and amended on November 15, 2011 and does not otherwise reflect events occurring after such original filing and amendment of the 10-Q Report. This is the first year of XBRL compliance for K12 Inc. and as this is our initial XBRL submission, we are using the 30-day grace period allowed for such filings.

Pursuant to Rule 406T of Regulation S-T, the interactive data files contained in Exhibit 101 are deemed not filed or part of a registration statement or prospectus for purposes of Sections 11 or 12 of the Securities Act of 1933, as amended, are deemed not filed for purposes of Section 18 of the Securities and Exchange Act of 1934, as amended, and otherwise are not subject to liability under those sections.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

Date: December 9, 2011