Opportunity to learn is considered an important contributing factor in learning outcomes. In some of the latest international comparative studies of mathematics achievement, such as SIMS and TIMSS, painstaking efforts have been made to find out what the participating students' opportunities to learn mathematics had been. However, there have been problems with relating the findings to student outcomes. This article approaches opportunity to learn in three different ways. Among these approaches, an item-based analysis of textbook contents resulted in fairly high correlations with student performance at the item level in TIMSS 1999. This implies that even a quite simple analysis of textbooks can produce valuable information when looking for explanations for student achievement in mathematics.