IB schools are not supposed to stream, but I know one that does in maths. Streaming seems to be out of fashion.
it's useful though if you have some kids who are really good at the subject and some which are not. Not really fair to hold the bright ones back with the teacher having to focus more attention on the not so bright ones.
And I'm speaking from experience - I was one of the not so bright ones in Maths and was in the bottom group. I can't see that there would have been any benefit to me being in the same group as the Maths geniuses - and I can't see that it would have been of any benefit to them either.