School Bullying

My son is a P.1 Student studying in ESF school, he was bullied by students from other P.1 class. They pushed him, glared at him and used bad sign language to him whenever they saw him in the playground. he was scared. I have informed his class teacher. They have stopped their naughty behaviour for a while. Yesterday and today they bullied him again. This is annoying. I don't know what to do. Please advise.