The primary school nearest to me has more pupils but all of the classed are mixed ages. So reception and Y1 are together, then Y2, Y3 and Y4 are all together and Y5 and Y6 are together.
I remember being in a mixed class throughout my primary schooling and it was never a problem for me, probably a benefit in fact (I was a clever kid so usually did the work for the year above, kept me stimulated), but for kids who need more focused attention and guidance I can imagine it's a tough environment. If a teacher is covering multiple curriculums and topics for kids of a huge range of abilities and levels, I'm sure it's really hard to provide that 1-to-1 attention that some kids do need to progress.
Poor Alfie. Even at school he's not likely to be getting the support he needs, and we know he's definitely not getting it at home. I think any regular parent would be doing their best to either move schools to provide him with more support or make sure he's getting what he needs at home to supplement his learning.