They have stopped because they have been abused. They were originally supposed to show end of key stage progress at different ages, as an A at 6 years old is not the same as an A at 13 years old for example. So 1-2 at key stage 1, 3-4 at key stage 2 and 5-6 for key stage 3. But then league tables got in the way and primary schools had to be seen to do doing better and stretched it to level 5 at the end, which was not the same level 5 originally meant for end of Year 9. Then secondary schools had to be seen to be doing better and more 7s and 8s were handed out. Then OFSTED used it to measure schools and sub - levels came in and randomly came up with the idea of the "2 sub-level a year" progress. However, there was no standardisation. A level 4a at one school or one subject, is not the same as a 4a in another school or subject, for example. It is a good thing on the whole, but as usual, the DfE have been very vague as to what will be replaced.