HADLEY - Last summer, three families living in different towns were very disappointed that they were unable to send their children to Hadley schools under the "school choice" program.

So they all solved the problem by moving to Hadley, enabling the children to go to school there.

"That's a testament to our school system," said Tracy Kelley, chairwoman of the School Committee. Superintendent Nicholas Young said he hadn't seen any other examples of education relocation since he took the job in 2001.

Hadley's public school enrollment has increased by 12.4 percent since 2005-06, from 635 to 714. During that same time, Amherst's enrollment has declined by 11.4 percent, from 3,341 to 2,959.

More than half of Hadley's growth is attributable to an increase in "school choice" students, who now total 75, or 10.5 percent of total enrollment. Amherst admitted 71 secondary students from other towns under "school choice" last year, a decline from 108 in 2006-07, and does not accept them at the elementary level.

The Hadley School Committee is trying to decide how wide to open its doors. On the one hand, each "school choice" student brings $5,000 to the town and increases diversity, Young said. On the other hand, there are concerns that too many students could cause an increase in average class size.

"We've been careful about the program, and accepted students incrementally," said Young. In 2008-09, there was a spike from 53 to 70, largely because several families moved away from Hadley but wanted their children to stay in school there, even if the parents had to provide their own transportation, he said.

Hadley accepts "school choice" students only in grades where the numbers of town children are low enough to accommodate more. The average class size in Hadley is smaller than in many districts, Young said.

Sometimes there are lotteries to determine which children seeking admission from other towns can come to Hadley schools, and there are many more requests than the town is able to honor. In one case, a parent was willing to have her child move back a grade if that would enable the child to be in the Hadley schools, but Young declined the offer.

School Committee member Robie Grant said that many parents feel strongly about the educational importance of small class sizes, especially in the lower grades. "It's a community values issue," she said.

School choice is "one of the few places the School Committee has discretion about raising money," Young said. Hopkins Academy now has 30 more students than it used to, and this has allowed it to expand its offerings, he said.

While the number of "school choice" students coming to Hadley has increased from 32 to 75 in the past five years, students living in Hadley but attending school elsewhere has gone from 23 to 37. The number of Hadley children attending charter schools has increased from 10 to 25, largely because of the arrival of the Pioneer Valley Chinese Charter School in Hadley, Young said.

The School Committee decided to participate in the "school choice" program next year, but deferred a discussion of how many seats to make available.