Chess.com has a great solution for this problem

Some sites can be blocked on school websites or computers. Teachers can add chess sites such as Chess.com to the list of banned sites to prevent their students from playing chess in class or at school. Chess.com has found a very good solution to this. Now you can go to plansformyfuture.com and play chess in secret. I mean, who wouldn't want to play chess? I do (: 

happy chess for everyone!