There has been much debate recently about how to judge whether a school is 'good' or 'outstanding'. Some of the evidence presented in this debate referred to the percentage pass rate of GCSE Grades A-C or in other words, the attainment of the school. The question was asked about how a school with a pass rate of 54% could be judged outstanding.
In my opinion, attainment is a false measure of the effectiveness of a school. The key measure of effectiveness should be progress. If you imagine two window cleaners working on a very tall building. One of them starts at the ground floor and the other starts at the 60th floor. By the end of their shift they have both reached the 80th floor. If we are measuring effectiveness by attainment then they both have done an equally good job. However, the cleaner that started at the ground floor has clearly worked harder and made more progress. He is therefore more effective.
Similarly, imagine there are two schools which both attained 50% of children achieving Level 5 in writing at the end of KS2. If in one of the schools, the children left KS1 at Level 2c and in the other they left at level 3, which school is the most effective? Clearly, the first one is more effective as the teaching in that school has had more impact on the children as they have made more progress.
If we measure schools by the progress the children make then it is a level playing field. Particularly if we build in some contextual information. Measuring schools by attainment is not fair to those schools that operate in more challenging circumstances and allows schools in privileged areas to be complacent.