Groton - Think of it as the kid version of tossing extra change into the tip cup after buying a cup of coffee.

At Pleasant Valley Elementary School, as in many schools in eastern Connecticut, teachers hand out small paper slips to recognize students for good behavior.

But the Pleasant Valley staff wanted to keep kids interested, so this year they gave slips a value, then opened a school store at lunch time where the children could use them to "buy" something - a gel pen for 25 slips, for example.

Then the teachers went further. In April they gave kids the option to donate their vouchers to charity by placing a bucket on the school store table. Each slip equaled 10 cents, redeemable by the Parent Teacher Organization, for the Groton Animal Foundation.

Fourth-grade teacher Elena Lockett, who worked with the group that came up with the idea, said she hoped they'd collect $100 from students in a month and another $100 from families and staff. They raised that in one day. By the end of April, the 289 students had donated more than 2,800 vouchers. The school sent home notes to parents about the program, and donations arrived in $50 bills and envelopes with coins inside. The total: $710.

"I guess I'm surprised to see that we got that much, because I'm still new at this school," said Devonte Conway, 11.

Devonte said he bought a mechanical pencil for 10 slips, then dropped the rest in the bucket. Student after student did the same thing with their "change."

Each grade has a designated day to visit the school store, Devonte explained. "You have to get up here fast, because if you don't you have to wait until next week," he said.

The school's next charity is the Sandy Ground project by the Where Angels Play Foundation, which is building playgrounds to commemorate each of the 20 children and six adults who died in the December 2012 shootings at Sandy Hook Elementary School in Newtown.

Superintendent Michael Graner said all Groton schools will raise funds for the cause, but Pleasant Valley got a head start. "Here, the children are doing it," he said.

Foundation Director William Lavin met with Graner and Groton's principals last month. On April 27, the foundation opened a playground behind the Mystic YMCA to commemorate the life of Grace McDonnell, one of the first-graders who died at Sandy Hook.

The idea behind the Sandy Ground project is to have each community "pay it forward" by raising money to build the next playground.

At Pleasant Valley, the hope is to create a fundraiser through which children give of themselves rather than collect money from their parents and bring it in. "This is really about what they have to give," Principal Kathleen Miner said.

The school program that teaches respect, responsibility and readiness to learn - and now charity as well - is called "Catch a Wave." Teachers "catch" kids doing something responsible like helping younger children on to the bus, and acknowledge it with a special slip. Each paper slip has a wave on it.

Lockett, the teacher, said the staff will be "discreet and sensitive" when explaining the Sandy Ground cause, and will focus on the playground.

Julia Allen, who volunteers at the school store, said one boy brought in wave slips from his entire class.

"I think kids just naturally have giving hearts," she said.

d.straszheim@theday.com