How to do it in maths? OK, well first of all with your son, if it were me I'd be making no assumptions at this age other than maybe he needs more practice than others in learning to count to 20, and making sure that he gets this practice both at school and at home - same for other very specific areas of maths where he seems to be behind his age group. Also you'd have to work out what your son does find diffult about "counting to 20" .... what does it mean? And then move on from what he can do and work in small steps on the next steps in a fun way but that involves lots of overlearning.

Then, when planning lessons for the whole class, yes you would need some easier and "harder" tasks, but you don't have to assume that every lesson on every maths topic will be delivered "like this to the below average group", "like this to the average group" and "like this to the above average group". You could have some more open ended work which each child could complete to the best of their skills and knowledge at the time and which would give everyone a "stretch", and some more "closed tasks" of increasing difficulty and some children would get further than others on them? Just a thought. But I've never taught maths to this age group. Frankly I would find it a complete nightmare and none of them would ever learn a thing whatever group they were in.

The trouble is that with the fixed groups based on "ability" at this young age is that, even if the groupings are kind of right in some respects, they cannot be right for each and every maths topic. However you fix your groups you are going to get somehting wrong. e.g. You are going to get children in the top group who can't tell the time for toffee, for example, and children in the bottom group who are great on drawing in lines of symmetry on 2d shapes, or doing reflections, or solving a problem with equipment etc.

I really don't see how at this age where every child will have very different maths skills how a "one size fits all" approach within three fixed groups can help any more than going mixed ability and allowing for the fact that in any one lesson you will have children at a wide range of stages in the topic you are trying to teach.

You are not going to change the school though. On a personal note I'd find some maths materials (both practical and theoretical) that your son enjoys and do them at home. I know Amber would say I was wrong, and to leave alone, and wait for the child to be "developmentally ready" but I'd be concerned if my child was in a "fixed group" school and he could not count to 20 by the end of year 1. Unless there was some severe learning difficulty I'd be assuming that he was quite capable and just not making the progress he could in a group situation and that some well thought out one to one at home would do the power of good.

Of course I could be completely wrong and the school might doing their utmost for you and your son and I have put my foot in it. Sorry if that's the case!!