In the third article, Törnroos advances a methodological approach for gathering opportunity to learn data that exhibits a high correlation with student achievement. The author compared three measures of the opportunity to learn with student achievement in Finland based on data gathered from the Third International Mathematics and Science Study (TIMSS): a measure of the proportions of mathematics textbooks dedicated to different topics, teacher questionnaires regarding topics taught and their duration, and an item-based analysis of the textbooks. The item-based analysis involved examination by a team of five researchers and mathematics/science teachers to determine whether items included in TIMSS 1999 were adequately covered in each textbook. The study determined that learning opportunity data required more than one year of data in order to generate strong correlations to student achievement. When this was done, Törnroos found that item-based textbook analysis yielded the highest correlations of the three alternatives. Challenges to the utilization of such learning opportunity measures to explain student achievement include factors such as instructional quality, differences in potential curriculum implementation (textbooks) and actual classroom topics covered, as well as the uniformity of national learning opportunity data. The author concludes by calling for similar studies utilizing international assessments in order to generalize the usefulness of item-based textbook analysis as a learning opportunity measure.