A student in my class is having surgery for osteoid osteoma, he’s 13 years old. I’ve not heard of it before. I know it’s not serious but what population gets this type of problem?

Osteoid osteoma, as you said, is not serious but it does cause a lot of pain, which is why surgery is done to remove it. Most often, it appears in children and young adults who are between five and 24 years old and more in boys than in girls. Usually, it is the long bones that are affected.