Yeah in my city it's mandatory to wear helmets while skateboarding/rollerblading/biking/scootering or whatever else you're doing. It is such a good idea to wear a helmet.
My principal's son, was snowboarding at my ski club (not a member, a guest) and was in the terrain park. He decided to go off one of the big kickers with no helmet or no spotters. So he did, and just as he went off, he saw that there were a few people in the landing area getting up after a minor fall. He tried to swerve his body and his board so he would miss them, but he couldn't, and he fell head first. He had to be airlifted to Sick Kids hospital in Toronto.. He was put into a coma for a long time (can't remember how long exactly) and forgot EVERYTHING. My mom and her friend went to go see him, and for the first time, he opened his eyes. It was only for a brief second though. He was fed through a tube, and he was basically in this coma, not moving, for a long time. Once he was out, he was still in the hospital, and they had to teach him how to walk again and partially talk. It was so hard for the principal, he had someone fill in for him for about a year. Then he went to rehab, and it took very long for him to recover. He basically fucked up a side of his brain or something and forgot basically everything. I don't think he had to retake classes because it was one side of the brain where it didn't include skills like that, I think.
Everyone in his family was going through so much pain and couldn't bear it. I remember the principal saying to my mom that he would never be the same again. That he would never be the same Sacha he knew him to be. You seriously don't know how horrible this was, for the kids, the families, the parents and just his friends and relatives who knew him. The whole school was in shock, for this was heartbreaking.
Moral of the story: ALWAYS WEAR A HELMET!!!!!!!!!!!!!!!