The government's expectation is Level 2 at end of Year 2 and Level 4 at end of Year 6. i.e. 2 levels progress each key stage. Silly heads will interpret this as meaning 1.5 sub-levels every year during Key Stage 2. Sensible heads will realise that children don't progress in a straight line. Ignorant heads will want to be "above average" and 'expect' 2 sub-levels a year. There are even a few moronic heads talking of 3 sub levels a year!