With the rise of large-scale academic assessment programs around the world, there is a need to better understand the factors predicting students’ achievement in these assessment exercises. This investigation into national numeracy assessment drew on ecological and transactional conceptualizing involving student, student/home, and school factors. Student factors comprised mathematics ability, gender, and year group. Student/home factors comprised mathematics tutoring, mathematics competition participation, computer support for mathematics, and practice mathematics tests. School factors included school-average mathematics ability, school-average practice mathematics tests and competition participation, and socioeducational status. These educational ecology factors were modeled as predictors of mathematics motivation. In turn, educational ecology factors and mathematics motivation were modeled as predictors of numeracy achievement. Data were drawn from N = 12,736 Australian elementary (Years 3 and 5) and secondary (Years 7 and 9) school students from 231 schools participating in a national numeracy assessment exercise. Multilevel structural equation modeling revealed that student and student/home factors (Level 1) and school factors (Level 2) explained significant variance in student- and school-level mathematics motivation. In turn, these factors explained significant variance in student- and school-level numeracy achievement. Findings hold implications for the nature, breadth, and depth of efforts aimed at improving mathematics motivation and numeracy achievement in large-scale assessment programs.