Personally, I wonder if one student will do it just out of spite and make everyone lose the 100 bucks. Like a kid whos been bullied and loner, he will start a fight to make sure all of the people who bully him will not get the 100 bucks.
Our elementary school offered to put kids' name in a drawing for a bike who perfect attendance at end of the year. I wrote them asking what about kids who can't help missing school like mandatory doctor appointments. They didn't do it anymore since I wasn't the only parent who complained.