Individual effort is controlled for in the study discussed: "each extra required maths course raised the annual income of black males by 15%". Of course, this study still doesn't make a strong case for causation -- the number of required math courses in a school is likely correlated with school quality, which is likely correlated with other socioeconomic factors.
Huh? How do you infer that individual effort was controlled for by quoting "each extra required maths course raised the annual income of black males by 15%"?
