The paper attempts to investigate the influence of textbooks on the results of international assessments such as TIMSS [Trends in International Mathematics and Science Study] and PIRLS [Progress in International Reading Literacy Study]. It tries to consider the role and impact of school textbooks on PIRLS and TIMSS performance across countries. As the research finds, the predominance of analytical, opinion-expressing, inferencing and evaluative categories in the school textbooks significantly favor the scores in PIRLS across the countries observed. In the case of maths, probability, data analysis and algebra problems are most predominant items schoolbooks of high performing countries in TIMSS. Advanced level analysis, integrating and comparing data, as well as reasoning and analysis could potentially be significant contributors to TIMSS science results.