Planning Experiments in Science Education Research: Comparison of a Quasi-Experimental Approach with a Matched Pair Tandem Design

The planning of adequate control groups is a central aspect of educational research.
Didactical studies, however, are often field studies encountering many problems of
everyday classroom teaching? Recent research has indicated that teachers and their
beliefs have an enormous influence on learning and retention. Taking this line of
evidence further, a devil‟s advocate may emphasize that differences in treatmentcontrol
designs may be not a result of the different instructional strategies but reflect
differences between different teachers. In this study, we try to sort out this kind of
“teacher effect” by comparing two approaches of a complex treatment-control group
design. In the first approach we compare treatment and control groups that were taught
by the same teachers (labeled „matched-pair tandem design‟), and in the second
approach we compare the control group with an unrelated treatment group where
different teachers taught the treatment groups („unrelated design‟). When comparing
the „matched-pair tandem‟ design with the quasi-experimental approach, we found i)
similar patterns in both educational experiments, and ii) higher effect sizes in the
unrelated, quasi-experimental design.