ReallyTired, surely the scaled score gives you the information you need for comparison purposes? 115 is on a scale from 80 to 120. 100 isn't an average score because the scores are designed to allow governments to compare year to year but it still gives you a very clear guide.
Spooninthebin, it could be an issue with the teaching if the teacher isn't used to differentiating under the new curriculum. It's true that evidence suggests that while keeping all children together is hugely beneficial to the vast majority of learners, it can have a negative effect on the absolute highest. However, there's absolutely no reason why this needs to be the case based on the curriculum. Some of my high achievers took a while to adjust to the new curriculum because they're used to acceleration over depth -- and, because they were in the crossover between curricula, sometimes had already covered what was being taught. However, they're actually a lot more challenged and much better mathematicians now.
Take a year 4 objective: multiply 2 digits by 1 digits. Accelerating into 3 digits by 1 digit or 2 digits by 2 digits is really just another trick to perform for these highly confident mathematicians.
Whereas these questions link to the same objective as their classmates but at greater depth:
If you know 94 x 8 = 752, how can you use this information to calculate 95 x 8? 47 x 8? 326/8? Explain how you know. How many other facts related to this calculation can you derive in 2 minutes?
36 x 8 = 2448 - what's the misconception? Explain it and find the correct solution. (Peer teaching is great for developing this skill which is the advantage of whole class).
Replace the ? with digits: ?8 x 4 = 15?
3? x ? = ??3 -- how many ways could this be true? Work systematically to prove your answer.
Jim and Tim a dice to generate some random 2 digit number by 1 digit number calculations. Jim says, "if the answer is even, I get a point. If it's odd, you get a point." After 20 goes, who do you predict will have more points? Why? Try it. What do you notice? How can you explain your findings?
You're not looking for progress in new headline content but in developing skills -- conjecturing, generalising, working backwards, drawing on experience to solve problems, hypothesising, working systematically etc. etc. You should see the progress rippling through computing, geography, science etc.