- Differential school composition effects across the conditional reading score distribution, with students in the lower quantiles achieving the largest test score gains.
- Mathematics results suggest that high- and low ability students benefit equally from attending schools with a better student intake, and most results for science are only marginally significant.
- Results imply that mixing students of different background could improve equity of achievement for both reading and mathematics; however, the average skill level would improve only for reading literacy.
- In mathematics, mixing students would not raise average outcomes, because the detrimental effect on students in the higher quantiles would offset positive effects on those in the lower quartiles.
- The level of SES at the school appears to be significantly related to test scores in all three subjects, but there is no conclusive evidence as to whether the heterogeneity of the student body affects test scores.
- The effect of school composition is of similar magnitude for each test subject, though slightly smaller for reading skills when information on the learning environment is entered.
- For reading, and to some degree also for science, higher school-SES raises test scores at the lower end of the achievement distribution, while students at the (very) upper end are unaffected.
- School SES matters for high and low ability students alike.