I stumbled across this – Educational achievement in English-speaking countries: Do different surveys tell the same story? – from 2004. It’s getting on a bit but seems unlikely to be off the mark given the trends in England over the past decade and the move there toward greater inequality across the board.
The first graph, above, which combines data from England and Scotland, reveals the UK (GBR) to have a larger attainment gap (dispersion), between those getting the lower scores and those getting the higher scores, and to have below median achievement overall. In the same top-right quadrant (unequal and failing) we find the USA as the worst performing and in the bottom left quadrant we find more equal and successful countries such as those in Scandinavia, Canada and of course Finland.
However, in a graph where, by chance, only Scottish data was available, the picture changes dramatically:
In the above graph comparing the attainment gaps in maths and reading of those children whose mothers did or did not complete upper secondary education (to Year 6), the GBR data (Scotland only) places the UK among the more equal countries in the bottom left quadrant, where the gap was narrower for both subjects.
The report notes tellingly, with regard to the above:
No parental education data were collected by TIMSS in England so the UK difference for TIMSS in Figure 4 is the value for Scotland alone. Comparing means for Scotland and England in PISA suggests that were parental education to have been collected in TIMSS then the difference for the UK would have been a fair bit larger.