The Jonas Brothers treated elementary students in Los Angeles to an impromptu concert on Tuesday (21Sep10) as they handed out school supplies.

The singing siblings teamed up with stationery company Office Max to take equipment to the Los Feliz Charter School for the Arts - and they sent kids crazy as they unexpectedly took to the stage.

The school's project manager Amanda tells E! Online, "I thought some of the students were going to pass out! It was amazing, the boys were great. I've never met people so selfless. They were so interested in the school. We are very grateful to them and Office Max. Our teachers each got $1,000 worth of school supplies too."

The band also posed with fans and signed autographs - and Joe Jonas admits he was happy to be part of the venture.

In a post on his page, he writes, "Starting the day off surprising some kids w (with) OfficeMax gifting them some school supplies. Feels good to give back."