The table of 'effect sizes' in the book clearly identifies the effects of one element and the effect size of another on student achievement, but what consideration is given to the inter-correlation between those areas?

Full Question: The table of 'effect sizes' in the book clearly identifies the effects of one element (e.g. direct instruction) and the effect size of another (d=0.82) on student achievement, but what consideration is given to the inter-correlation between those areas identified? As one example, teacher-student relationships has an effect size of d=0.72, and reducing class size an effect size of only d=0.21. However, what effect does reducing class size have on the ability for teachers to develop deeper relationships with their students?

Answer: We agree that the overlap between areas is critical. It is not as simple as combining the influences to get an increased effect. It is important to create a story about the underlying common parts such as success factors, student assessment capabilities, knowing thy impact etc.