if any of your friends is not ready to share his ideas in class, fearing he might be wrong or he is not joining to play with others thinking they don't like him, how can you help him?
you should support him in the social anxiety he has and assist him by assuring him it will be okay of the answer might be wrong because not everyone gives the right answer. He should not feel judged in any way and should be slowly but surely pushed towards fixing his social anxiety without pushing himself to far that he becomes unsure of everything
