Washington Post Co. shares fell almost 7 percent Friday as a cloud of uncertainty gathered over its biggest revenue and profit driver: the Kaplan education business.

The Post Co. said proposed changes in federal education policy would have an uncertain effect on Kaplan.

The concerns that lawmakers have about the type of for-profit college that Kaplan runs were underscored this week. The U.S. Senate heard testimony Wednesday on a Government Accountability Office investigation that found questionable recruiting tactics, high loan default rates and low graduation and job placement rates at for-profit colleges. Kaplan and 14 other institutions were singled out for criticism.

The Post Co., which is selling Newsweek magazine as it pulls back from its traditional identity as a publisher, has relied on Kaplan for several years now to drive growth.

Second-quarter results reaffirmed Kaplan as the company's main engine. It booked a 15 percent increase in revenue and an 88 percent jump in operating profit.

Overall, the Post Co. reported a nearly eight-fold jump in net income to $91.9 million, or $10 per share, for the three months ended July 4. That's up from $12.2 million, or $1.30 per share, a year ago, when the company absorbed $56.8 million in expenses tied to an early retirement program at the namesake newspaper.

Revenue climbed 11 percent to $1.2 billion from $1.08 billion a year ago.

Along with growth at Kaplan, the Post Co. also benefited from a rebound in spending on television advertising.

Revenue at the Post Co.'s six broadcast stations climbed 24 percent to $82.6 million as demand for commercial time picked up. Operating profit more than doubled to $29.8 million.

The uptick in spending on television ads — an industrywide trend — has not extended to print media, though newspaper advertising declines have eased since the bottom of the recession.

The Post Co.'s newspaper division saw a modest 2 percent lift in revenue despite a 6 percent decline in print ad sales at its flagship daily. That and lower retirement expenses helped the newspaper division narrow its losses to $14.3 million from $89.3 million.

Revenue rose 2 percent to $190.6 million at the company's cable division, while operating profit climbed 10 percent to $43.8 million.

Post Co. shares tumbled $27.39, or 6.7 percent, to $381.22 in morning trading.