A lot is said about CATS identifying underachievers, however it can work the other way. My daughter's prep apparently used CATS to inform secondary school recommendations, but did not explain this. Instead we were left reeling when she was discouraged from applying to the same relatively academic schools as her class peers, and the prospect of a weak school report.
Lots of panic and some deadlock, though in the end we got school support and she did just fine, getting 4 out of the 5 selective indies she applied to.
Interestingly she did amazingly badly on the Tiffin test, even though she thought she had done well and failed to get a selective place at our local CoE school. We had her tested (expensive) and it was explained that the overall score was only an average and as such was a poor predictor for a very one sided child. DD will be fine when it comes to A levels, where she can choose her preferred subjects.
She is really flying now, and actually in all subjects. I suspect that her previous school was cautious about putting her in sets which matched her exam results because she had such low CAT results. The secondary, presumably because it has already selected its pupils, does not seem to use the same approach (plus they have the in-depth assessment we passed to them) and she is delighted to get away from the typecasting and be seen as one of the "clever" ones.
We still don't really understand why she is so bad at CAT tests, and feel it was a pity that the prep did not discuss the results with us before making their minds up. (Her teachers, in contrast were a lot more positive and encouraging because they knew her in class.) The idea that a school would use these tests, rather than achievement, for setting, is worrying. I accept that it is a way of picking up under-performers and making sure they don't get lost, but over-performers should not be disadvantaged just because a test suggests they have less potential.
I would ask to discuss the results and the implications.