It is a commonplace observation that being successful at almost anything is due largely to hard work. The implication for "human capital production functions" (Hanushek 1986, 1987) is clear: holding ability constant, cognitive-skill progress is determined by time-on-task multiplied by the quality of this time spent by the student, that is, the concentration or efficiency with which the time is spent. More formally, skill at timet equals that at time t - 1 plus the gain during the elapsed time interval, and this gain equals the time-on-task during this interval times the intensity of effort (or quality of concentration) during this effort. That is, conditional on student ability and the quality of teaching,
achieved skill(t) = achieved skill(t - 1) + gain(t, t - 1), (1) and
96 Habits and Styles
these key inputs-time-on-task and concentration-separately for population subgroups. Surprisingly, however, this has not been the case, and this despite the fact that anecdotes abound regarding the schoolwork diligence shown by Asians, as well as the schoolwork carelessness shown by African-Americans. No doubt one explanation is the relative difficulty in collecting such information. Few researchers have been able to ask students to report the time they spend on schoolwork, even if the results could be credible. And those who have typically lacked any measure of the quality of that time, including the most important aspect of such quality-the student's ability to concentrate in class.