DS at prep was in a prep/1/2 composite class, year 1 was prep/1 and year 2 is in a 2/3/4 class.
DD has been in prep/1.
The only one I didn't like was the prep/1, when he was the older part of the composite. The teacher didn't challenge him enough in maths (he is advanced in maths), and he didn't get enough help in English which he is not so good at. I think that was mainly the fault of the teacher though.
Otherwise, I love the comp classes. I have asked for him to be in a 3/4 next year, when he is grade 3.