If classroom disruption is getting in the way of teaching, causing able children to fall behind, have you raised this with the teacher or further up in the school? Is your son unhappy, bored in the classroom, worried about the behaviour of others? I would keep a close eye on this, regardless of how your son is doing academically.
Is there a parents’ evening coming up, in which you could ask how ready your son is for the SATs, and ask for guidance on which specific areas he could do with working on?
Of course, KS1 SATs are important to the school, but much less so to the children. There is a logical case (which I admittedly would be reluctant to pursue with my own Y2 child!) for leaving the school to it, and waiting to see the children do badly in the SATs, which will soon highlight the problem to the Head etc.! However, in your situation I’d want my child to do well.
While I don’t have concerns about my DD’s teaching at present, I am aware that they cover a lot of material in maths in Y2 without a great deal of time to practise each concept, and I want to make sure she has grasped everything fully. I recently found what looks to be a useful year 2 workbook. If she can do all of this confidently, I will feel she will have covered the KS1 maths curriculum. I’m watching to see which sections take longer, and intend to provide additional practice for her in those areas.
It looks as though the same company does a ‘workout’ for comprehension, and another for SPAG (I haven’t looked at these as they are my DD’s strong areas). I’m sure there are other publications that do similar things as well.