Does increasing time spent in class improve student performance?

Their findings indicate that while increasing the time spent in class did improve students' average performance, effect sizes were small. The increase in lesson time was shown to increase average PISA test scores in reading, math, and science (effect size between +0.04 and +0.06 for one additional hour per week). However, these results differ according to student ability, with a widening gap in performance between low- and high-performing students. The researchers suggest this is because the additional teaching time was used to teach new content, and that lower-performing students may not be able to cope with this additional content. They recommend that when policymakers consider adding additional classroom time, they consider how this time is spent. Different students have different learning needs, so the content of the extra lessons, rather than the time, is more important to improving student performance.