Ahh, I can help you understand this. I am a teacher in a year 2 class, plus a parent of a year 2 child!
Basically, when a child does the 'formal' SATs paper for level 2, the number of questions correct will indicate whether they have achieved a 2a, 2b or 2c. You can get around 8 questions incorrect and still be a 2a, though it depends which SATs paper was done as the marking scheme varies. Schools can choose from 2 different papers at the moment. If a child achieves a level 2a, it is usual for them to then sit the level 3 paper. There is a pretty low mark, maybe about 12, for the child to achieve a level 3. It is not divided into a,b and c. It is simply a level 3. However, teacher assessments are different, and your child can be teacher assessed at 3c, 3b and 3a. Actually, you could assess your children, and SHOULD if necessary, into the level 4's. It would be unusual for a child to get 100%, i would be amazed. There is always an area of discomfort, or a misunderstanding (ie, the question says tick the cylinders and the child ticks one and turns over, without realising there were two to tick!) so I would never expect that. I think I have had one or two children do this. My own son is excellent at maths, he only got one question incorrect on the practice paper we did in class. However, on level 3 I encourage the children to attempt about 20 of the 30 approx questions. I know that several of the questions are beyon what has been taught in class, so just leads to demoralised feelings so I instruct which questions to attempt and they tell them they can have a try at the others after. I would expect about 10 children to have a try at the level 3, and typically 8 of them will achieve. However, teacher assessment may over-ride SATS anyway. If a child performs poorly, showing a level 2c for example, but I believed through assessments she was at 3c, I would sumbit her level as a 2a. Or if a child had a flukey go at a test and got level 2a, but typically worked at level 2c, I would submit 2b. Over asssessing is just not fair. It puts presure on child.
You dont say what subject the 3c was in relation to? Diff levels for reading, writing and numeracy apply, no child would be consistently same (well, its unusual) and its expected a progress of 2 sub levels per year (so i assume your daughter started year 2 at a level 2b, so 2 sub levels take her to 3c). However, her previous teacher may have over assessed her, so now she is struggling to show that progression. This is common!
You dont say what SATS papers you give her, but the current 2 in use are very different to the purchasable materials that call themselves 'practice papers' eg Letts and so forth. The best you can use are past papers/ We currently use 2007/2009 i think, but you can get 2001/2003 papers which are quite good. However, I would strongly avoid any home practice, school will take care of that! It is not a big deal and she really shouldnt feel any pressure. Thing is, a 2b is expected and if your child is a 2a, you should be delighted she is doing so well.
The reason the level 3 paper cannot gie her a higher score is the content of the questions- there is a huge leap between level 3 and level 4. In order to be a secure 3, you would need to demonstrate some level 4 skills, which wouldnt actually be expected until year 6. (level 4 i mean) so a difficult one. It isnt necessary and doesnt gain anything for the child. It is pretty much irrelevent. It is for the government to identify vulnerable groups, and poor teachers/schools, rather than use the info to teach the individual children if you see what i mean? When your daughter starts secondary school they probably wont even look at her levels! They will give her CATS tests which are completely different!
Year 6 SATS can be seen as more of a big deal, but again they dont really mean anything to the inidividual children. No doubt will be all techer based assessments by the time your child is 11!
Dont stress or worry as your little girl will start to think she 'must' do well and things. bless her. I hate SATS andstrongly believe they should be replaced with ongoing assessment as they have in Wales.But i hope i helped clarify anyway!