Hi satdown:
I agree with many who have posted.
Talk to the school - Don't wait for the next parent/ teacher meeting, which may well not be for several weeks. Contact the teacher and say that you are concerned and arrange to discuss what they feel the reason is for slow progress. It may be what's holding your DC back is he/she never fully mastered the times tables to x10 (or x12) and so is strugglig to work out that calculation and then running out of time on these standardised tests. They may have some good ideas on what you can do.
Try looking into what you could do. A tutor may be too expensive but on-line tutorials may be a solution. Both Mathswhizz (www.whizz.com/) or Mathsfactor (www.themathsfactor.com/ - which we've used to great effect for DD1 started late Y2 and have carried on - now Y4 and in top maths group) are available.
If speed is the issue - I highly recommend a free open source computer game called Tux of Math Command (tux4kids.alioth.debian.org/tuxmath/). It's a bit like the old video game ASTEROIDS - the sums come down the screen and you blow them up by typing in the correct answer. You can select the ability level (easy to hard) and the type of problems to review.
Really look hard for what the issue may be. It could be that those number bonds (so understanding quickly that if 7 + 3 = 10, then 17 + 3 = 20 and 27 + 3 = 30 and so on. But also that in subtraction if you have 35 - 9 you can quickly do the work in two steps - so take away 5 to get 30 and then take away 4 to get the answer, which is 26 - again using those number bonds to get to work out 10s).
If your DD is now 3a - then he/she isn't too far off from the Level 4 national target for KS2 SATs - and it sounds like if you spent a few months really working on maths and investigating what the stumbling blocks are, you may be able to raise his/her attainment before the KS2 SATs. Certainly there is still time.
I think the way to look at it is that you DC sounds like they're doing fine in other areas - so a bit of extra time/ practice in maths can't hurt and it sounds like your DC isn't far off achieving the 'L4' on the KS2 SATs - and possibly if the problem is that fundamental understanding of number patterns and recall of number facts (multiplication tables/ simple number bonds/ etc...) isn't quite there, which is affecting the speed with which your DC is answering questions on timed tests. You may just find that speed is the issue rather than understanding how to 'do the maths'. To be fair to the school - if speed in answering questions is the issue, they may not have picked up on it in normal day to day lessons.
Hope that helps. Best of luck.