To understand heterogeneity in the effects of double-dose algebra across schools, the authors focus on two policy implementation features and their variation across schools. The first source of variation is the degree to which schools followed the cutoff-based course assignment policy. The second source of variation is the degree to which schools segregated algebra classes on the basis of students' prior skills in response to the policy. They ask the following research questions: (1) to what extent did double-dose algebra effects vary across schools?, and (2) how were these variations related to the ways in which schools implemented double-dose Algebra? (Contains 2 tables, 6 figures and 3 footnotes.)