Schooling matters. The authors’ professional pursuits for over twenty-five years have been focused on measuring one key aspect of schooling: the curriculum - what students are expected to study and what they spend their time studying. This documents their conviction that schools and schooling play a vital and defining role in what students know and are able to do with respect to mathematics and science. This research examines seventeen international studies of mathematics and science to provide a nuanced comparative education study. Whilst including multiple measures of students’ family and home backgrounds, these studies measure the substance of the curriculum students study which has been shown to have a strong relationship with student performance. Such studies have demonstrated the interrelatedness of student background and curriculum. Student background influences their opportunities to learn and their achievements, yet their schooling can have even greater significance.