Meta-Analyses and Descriptions of Illustrative Studies

In the third chapter an inventory of meta-analyses of OTL effects (association between measures of OTL and instructional alignment with cognitive achievement outcomes) is presented. This leads to a first impression of the average magnitude of OTL effects. The evidence from meta-studies that reviewed OTL effects appeared to be less solid than was expected. Leaving out a strongly outlying result, the OTL effect-size (in terms of the d-coefficient) compares to other relatively strong effectiveness enhancing conditions at school level, at about 0.30. One of the meta-studies was more specifically oriented to implications of high stakes tests for content selection in teaching. Next, seven case-study descriptions of illustrative OTL research studies are given, spanning four decades of research. The illustrative studies provide an impression of the diversity in emphasis, with exposure of content taught, and alignment between different curriculum elements (like standards, textbooks, taught content and tested content) as two different kinds of independent variables.