Waltham —   Gann Academy has received the largest gift in the Jewish high school’s 13-year history — $12,250,000 from a small group of anonymous donors. As with many such donations, there is a restriction. But this one is different. The money must be spent to wipe out the school’s debt.

Headmaster Marc Baker said the Waltham school owed that amount from when it purchased its 20-acre campus and constructed its 105,000-square foot school in 2002. The initial cost was $15M, and the school was slowly paying down the debt.

“We own our building and campus outright and have no outstanding debt,” said an elated Baker who telephoned the Journal between flights to Israel Wednesday morning, November 18. He was on his way to accompany home 35 Gann Academy students who had been studying at the Alexander Muss High School in Hod Hasharon for the past three months.

“It’s rare for donors to use their gifts to pay down debt,” Baker said. “People like to see their money going to new things: buildings or directly into programs. To have the foresight to see how critical it is that we should be secure for the future is huge financially, psychologically and existentially. It puts us in a dramatically different place.”

An immediate result of the gift, which had been expected, was to offer more financial aid this year — $2 M. The school will continue to offer generous financial aid awards in the future, he said. With full tuition at $27,700 annually, aid is crucial. Forty percent of the students receive it.

For the school to have no debt means that the money that would have been used to pay it down will now go toward the direct benefit of the students.

“To not have to cut teachers, to keep teachers’ benefits and to take small steps to improve programs,” Baker said, is the result. “Without it, we would have to decide where to cut to stay afloat. Now we can build the endowment” which is now between $5 and $6 million.

Baker said the school is healthy, with an enrollment of 316 students in grades 9 through 12. In the spring it graduated an unusually large class — 90 students — so its incoming freshmen, numbering 70 to 75, didn’t quite make up for the loss.

Freshman Katrina Kagan of Salem is one of four 2009 Cohen Hillel Academy graduates to matriculate to Gann this school year. For her mother, Marina Kagan, the $12.25 M gift came as a surprise.

The fact that the school will use the funds to bolster financial aid, she feels, is positive.

“That’s wonderful,” she said. “It will give more kids the opportunity to go there.”

Both Katrina and her mother love the school even though Katrina leaves the house before 6:30 a.m., catches a bus bound for the school in Vinnin Square and doesn’t return home to the North Shore for another 12 hours. Academics end at 3 p.m., and then Katrina is engaged in after school activities.

The transition, admitted Kagan, was hard for Katrina.

“It took her a long time to get used to it, but she loves it and has lots of friends. It has helped her in being organized. She doesn’t waste time,” Kagan said. She also had good words for Cohen Hillel, which prepared Katrina so well that the 15-year-old was in all honors classes.