Take pictures and keep a record of the incidents. Also request a follow up meeting in 6 weeks or so. Do not accept "boystrous behavior" or "isolated incidents" as a justification. If they say it is not happening, then I would start to worry. Ask for the school behavior and antibullying policy and ask about the behavior stage the other boy is. Remember you are not doing anything wrong. Sometimes (most of the time in our old school) they try to make you feel as the problem. You are protecting your child. He deserves not just being safe at school, but also feeling safe at school. I hate bullies and I hope your situation gets resolved asap. Good luck.
I would definitely bring it up with the teacher again as it is clearly not a one-off. Don't by shy or fobbed off - this can not be allowed. Schools are generally pretty good at dealing with this kind of thing.
My son is four , in reception and young for his age . He can be quite sensitive and shy . When he initially started in reception another older boy in his class kept pushing him , squeezing his face etc etc . I had a word with the teacher should I thought fairly defensive . It stopped until this week . Now he has come home with a mark in his groin after bring punched there and last night a mark on his back from the same child . I am quite a shy person too and don't like yo make a fuss but I mentioned it up his teacher who said she was sure it was just a one off and boys playing together . Now he has returned with another mark ..... What would you do ? I really like the teacher involved and don't want to be a trouble maker but cannot let this continue .