And if they all made the "expected" progress, everyone woud be on level 5s by the end of y6. It's really tricky - they might just be a level 3 at the end of KS1. You then put them in year 3 and there's the infamous year 3 dip as they settle into Year 3. A 3b and 3A has high demands to achieve. I've been there - all these "high" achievers from Y2 don't perform in Y3 and Y4.