My 20-month-old son bites other children in the kindergarden. He does it in the course of play, and sometimes he bites me, too. The kindergarden teacher says, this is normal, it's just an episode.
How can I make him stop?
This is completely normal at 20 months. Your daycare should have a strategy to remind him that he doesn't bite and distract him and to also look out for situations in which he is likely to bite in order to avoid them.
At home, if he bites you, I'd say "ow that hurt. teeth are for eating." If you are holding your child when they bite, I'd put them down for a minute. I'd also be careful to avoid any 'play' biting which can be confusing to toddlers. Just always be consistent in your response, and try not to be overly emotional.
We used the exaggeration of consequences treatment with our son when he went through this. A huge and loud "OW! That hurts!" followed by an immediate time-out addressed the situation at home in just a few iterations. He has never bitten anyone other than me or his father, though; he started with us when he was just over 15 months, and I'm guessing he didn't like the consequences enough to try it with anyone else.
At 20 months they aren't exactly SWARMING with empathy but they do have the rudiments, so maybe you could try something similar? If he bites, make a big deal about how much it hurts (don't roar in an angry way; roar in a pained way); if you can manufacture a few tears or at least a very wounded, sad expression, that might help him with grasping the 'oh wow, I guess not everyone enjoys this as much as I do' part of biting.
It sounds like his teachers aren't making a big deal out of this; can you speak with them and come up with a disciplinary structure that works for all of you? For example, when the children in my son's class act up (he's now 27 mths), they get to spend a timeout in the Cozy Corner (I swear that doesn't sound like a punishment to me at all (nap!) but I can see how being isolated from the rest of your peers while they play would be a punishment).
Mine did the same and I didn't let him bite me or anyone else, and he was sent to the naughty corner immediately, even if it was "just for the fun".
I have a friend who had really big issues with this and nearly got a legal issue for his girl biting to the blood the cheek of another girl at school. It stopped eventually.