Amber, this precisely sums up what DD's school does! They all take maths in Y10, even those who are struggling
Then in Y11, those who didn't do well re-take, while those who did start Y11 studying both further maths and statistics and a decision is made nearer the summer as to which (or both) of those they will sit.
This has worked reasonably
well for DD who will want to do science A levels but not maths as it takes her maths a little further than GCSE. But it's still a rubbish policy imho. I agree with everything Amber says.
KB, I think that's unduly harsh – statistics is a well established GCSE and from what I have seen of it is at least as tough academically as maths, albeit that it concentrates on just one aspect.