Shares of Washington Post Co., the media and education company partly owned by billionaire Warren Buffett, gained the most in more than two years in New York trading Wednesday, rebounding from a post-earnings slump.

The stock climbed 5.1 percent to $438.26 at the close, the biggest one-day gain since Oct. 29, 2010. The shares have climbed 20 percent this year.

Washington Post’s shares declined after the company’s earnings were reported on Feb. 22. The company posted a quarterly net loss of $45.4 million, or 6.57 a share, after writedowns and restructuring increased expenses.

Standard & Poor’s reiterated its hold rating for Washington Post shares Wednesday, saying the company could benefit from changes to California law. The state is considering a bill that would let California public universities accept credit for classes taught online. Washington Post’s Kaplan division, which accounts for most of its revenue, could be a candidate to participate, the firm said.