Does the progress slow as levels 3 and 4 are aimed for juniors. I'm wondering if levels 1 and 2 can be achieved early because the children have picked things up quickly but higher levels need to be taught so progress would slow down ?
Basically the first chart shows expected sub-level progress (against NC Levels in various Key Stages). [Do remember that NC Levels work C low ability or just working at this level / B average ability - fairly comfortably working at this level / A high ability - solidly working at this level and maybe showing elements of even higher ability level (i.e. 4a/ 5c)]
As you can see MN suggest that 2-3 sub-levels a year is about right for KS1 (years 1/2) and it slows to 1/2 sub-levels for KS2 (Y3 - Y6).
I am just a Mum, but as you suggest, I think that the increased difficulty & range of skills needed to be achieved mean progresses somewhat slows in KS2/ KS3 (Y7 - Y9 - so early secondary school).