One of the highlights of the school year at the Massachusetts Institute of Technology only lasts a few seconds but has a big impact.

Residents of an MIT dorm dropped an upright piano from their roof Thursday to celebrate the last day students can drop classes without having them appear on their college transcript.

About 200 onlookers watched as the piano crashed into a second piano, a baby grand, positioned on the ground six stories below for a better smash. People scrambled for souvenir pieces — keys, hammers, strings and splinters.

The tradition began in 1972 at the Baker House dormitory and has been observed sporadically until 2006, when it became an annual event, said Michael Plasmeier, who heads the dorm’s student government that organized the ritual.

“It was sort of not the official event. It was just some students who had a broken dorm piano that they threw off the roof,’’ he said. “Today, it’s much more formalized and announced and planned with everyone.’’

The piano drop tradition is so popular that astronaut Catherine Coleman, an MIT alumna, took a piano key from the event with her during a six-month stay at the International Space Station in a nod to the tradition, Baker House housemaster Jeffrey Hoffman, professor of aerospace engineering and a former astronaut, said.

The event “is always one of the highlights or maybe lowlights, as the case may be, and it’s a lot of fun,’’ Hoffman said. “The students basically run it, we’re just here to see nobody gets hurt.’’

The upright piano was rolled from a makeshift ramp on the Baker House roof. No piano has ever fallen on anyone’s head, organizers say.

“It’s done very safely, and it’s done with coordination with MIT security and emergency management office, and we set up a barrier well away from the piano, and then the people on the roof receive training from the security and management office,’’ Plasmeier said.

The tradition is a simple affair.