So says Josh Goodman at the Kennedy School:
I identify the impact of math coursework on earnings using the differential timing of state-level increases in high school graduation requirements as a source of exogenous variation. The increased requirements induced large increases in both the completed math coursework and earnings of blacks, particularly black males. Two-sample instrumental variable estimates suggest that each additional year of math raised blacks’ earnings by 5-9%, accounting for a large fraction of the value of a year of schooling. Closer analysis suggests that much of this effect comes from black students who attend non-white schools and who will not attend college.
Earnings where? Among which groups?
Yes, requiring math courses for other people increases my earnings. :) (Actually probably not, but it does increase the number of my colleagues.)