I've been looking at the secondary schools data in my area and am naively shocked at some of the differences in boys' and girls' performance at GCSE. One school, for example, has a 10-15% gap in the proportions getting 5 GCSES incl Maths; another is almost equal. All are inner-city, most with very high levels of disadvantaged pupils, with generally average results overall. Are these kind of gaps usual?