The harms of inequity are rarely overestimated: Comment on Marks & O’Connell 2021

Marks & O’Connell (2021)’s claim that an even-handed review of the literature shows that social and economic background does not matter to educational outcomes in ad- vanced economies, relies on questionable scholarship and grave statistical errors. Much of the evidence against the relevance of social and economic background rests on a stub- born misinterpretation of research that estimates gain scores, where the effects of student background on educational outcomes are much smaller because they are residual effects. A lot of time is spent arguing that parental education and occupation are poor measures of student background but it is not recognized that this leads to attenuated effects and thus argues against their thesis. Finally, there is a lack of serious engagement with the literature: cherry-picked numbers, summaries of studies that are at odds with the conclu- sions of the original authors and even two cases where thought experiments are presented as empirical evidence. Research into inequity does at times lack rigor in measurement and analysis, and not accounting for heritable abilities can confound and exaggerate the association between student background or school composition and educational outcomes, but our calculations suggest that the effect is more than offset by attenuation due to measurement error.