HOLLIS – There aren’t many high school classes in which a student can earn bonus points by hitting a teacher with a water balloon.

But John Boucher’s physics class at Hollis/Brookline High School is one of them.

Eleven years ago, Boucher and colleague Brian Maynard, who is now retired, put together the annual trebuchet day, held early in the morning on school grounds.

The event has been a draw for prospective physics students ever since.

The idea of aiming a water balloon at a teacher might be the appeal. Fifty percent of a student’s grade is based on construction and performance of the trebuchet – an ancient siege weapon that uses a counterweighted arm to fling projectiles.

The other half of the grade depends on the quality of entries in a journal that details how the device was developed and constructed.

On Friday, roughly 150 high school students brought 41 homemade trebuchets – and don’t call them catapults, which use tension on springs or ropes to throw projectiles – and set them up in the softball field before 7 a.m.

As in previous years, many students dressed in costume, appearing as knights, wizards, princesses and other characters associated with the era when the devices were once used in everyday life.

“The birth of this is I was writing a problem on the board,” Boucher said, explaining that students at every academic level study projectiles when they take physics. “I thought it would be cool to build (a trebuchet), gather data, play it up.”

The first project coincided with Halloween and a host of other holiday-related activities at the school, and over the years, it has been held at the same time.

“We take a concept and expand on it,” Boucher said. “Studying this way, we find a purpose.”

Boucher, who organized and ran the project this year with first-year physics teacher George Taliadouros, said other teachers brought their classes to the field to watch.

“They were so excited about it,” Boucher said, predicting that the event would convince other students to sign up for physics.

Hattie Bernstein can be reached at 673-3100, ext. 24, or hbernstein@cabinet.com.