Police said a man was spotted driving the van, which had been stolen the night before, at 10:30 p.m. on Crayne Street in Germantown. The driver, whom police did not identify, was arrested but the books were nowhere to be found.

Jean Warrington, who organized Historic Fair Hill's 2009 book drive and who owned the stolen vehicle, was relieved to have her van back but hopes the books will turn up, too.

The book drive is "a real benefit to the Clymer School," she said yesterday. "That's why we're so upset."

Police suspect that the cartons of books were tossed from the van, possibly dumped on the side of the road, said Warrington.

Clymer principal Kevin Parson said both faculty and students were disappointed.

"The robbery means 500 less books for the kids at this school," he said. "The books would have enriched their lives in many different ways."

For the past 10 years, the Historic Fair Hill's educational book drives have benefited various schools in the city. This year, Clymer, at 12th and Rush streets in North Philadelphia, was chosen to receive 1,500 books. The 500 missing ones were the last delivery.

"Our book drive is an effort to stress the importance of literacy," Parson said. "It gives kids access to good reading materials and helps younger students learn to read, and older ones read to learn. It is a valuable opportunity for all kids."

Budget cuts have tightened the school's belt on educational resources, so this week's robbery was especially untimely, Warrington said.

"The response this year was wonderful," Warrington said. "We got good books that were gently used, and they were all going to a good place."

Anyone who comes across 20 boxes of children's books that are marked "Fair Hill" should call 215-870-8348.