Please can someone tell me how much you’d expect someone to improve by over the course of a year at primary school/ KS1, as I have no idea at this level?
It's not as simple as that as there isn't a set results-ladder-based metric in place like there is with GCSE grades.
Generally speaking, a child who is assessed as working at the age-related standard has made the "correct" level of progress if he/she remains at the age-related standard for the next year group. Similarly, if they were greater depth at the end of Y1, they should also be so at the end of Y2. Children who move from the former to the latter have made more progress that year / Key Stage.
It has been impossible to quantify it at primary when using an end-point metric since the removal of "levels" 8 years ago.
I’m trying to get her to sit the exams this May (a year early). And wondering if they did do the exams next year what difference it would make?
When she sits the exams, whether this year or not or, indeed, whether she even sits the exams at all, will make no difference whatsoever. The results are not an official, externally varied measure. They are there purely to inform teacher judgement. In secondary terms, they are akin to an end of unit test or a mock paper: useful to have but no impact by themselves.
The mocks she did at school were 2015 SATS papers. At home she has done 2017-2019 papers and did much better (scored 104, 104 and 108). Don’t know why the school picked 2015 papers.
Possibly because they have found them to be a more accurate prediction tool or because they know that those papers are the ones parents are least likely to have downloaded and done at home, making the papers useless from a school perspective.
If you are having concerns about your daughters future at the school, having KS1 SATs data is highly unlikely to help you. What exactly are you worried about?