|Scharfenberg, F-J; Bogner, FX; Klautke, S: The suitability of external control-groups for empirical control purposes: a cautionary story in science education research., Electronic Journal of Science Education, 11(1), 22-36 (2006)|
This article deals with a specific effect in one external control group incorporated to account for any pretest bias in a more comprehensive cognitive achievement study in a gene technology lab (as part of a modified Solomon’s four-group plan). We monitored 12th graders (N = 117) in two external groups without any intervention: a one-test group (n = 55) and a three-test group (n = 62). Both samples participated in identical tests which quantified the relevant knowledge of the lesson unit applied in the main study. The three-test group yielded an unexpected increase in achievement scores. Subsequent analysis revealed two subsamples: one with no changes, the other with an increase (although without an intervention took place). A likely reason for the latter situation may lie in the role of the teacher(s) involved who might have wish to avoid potential negative results in his/her class. Consequently, we recommend the application of a modified Solomon’s four group plan in science education research in order to prevent the influence of teacher intervention in future empirical analyses.