Large-scale assessments provide important information about what students know and what they know how to do. However, this information alone is rarely enough. It tells us nothing about which students are performing well and which are struggling—or, more importantly, why. What learning opportunities have the students had? What resources are available to them inside and outside of school? What are their interests? What are their aspirations? What do their teachers and principals believe they can do? And how are these things related to the students' performance on the assessment? Background questionnaires—the questionnaires that students, teachers, principals, and sometimes parents are asked to complete when students take part in a large-scale assessment—can help us answer these questions.