The principal goal of attending school is to learn the coursework assigned by the teacher. This is particularly the case in middle and high school, where basic skills are assumed and each subject has a substantive focus. It is thus somewhat surprising that most studies of differential learning and its determinants ("educational production functions") have utilized basic skills measures such as ITBS and other standardized test scores instead of measures of learning assigned coursework as their dependent variables (Hanushek 1986, 1994; Murnane 1975; Summers and Wolfe 1977; Featherman and Hauser 1978; Jencks et al. 1979, 1983; Alexander et al. 1987; Entwisle and Alexander 1994). However, on closer examination this situation is readily comprehensible: the desired measures are almost never available. This is because the heterogeneity of what is taught in any particular subject at any particular grade level has precluded national data collection efforts from seeking to measure such substantive learning. Even within individual school districts, where assigned coursework by subject and grade level is presumably more homogeneous, few have undertaken the effort necessary to develop and uniformly administer tests of the students' success in mastering this material.