The aim of this study is to determine the effects of two versions of Computer-Based Feedback within a prevocational system of modularized education in The Netherlands. The implementation and integration of Computer-Based Feedback (CBF) in Installation Technology modules in all schools (n = 60) in The Netherlands is new. The main idea is that feedback in general has proven to be effective, but it has to be customized to the needs of the students. Therefore two complex variations of feedback are designed and tested in a population experiment following and extending a study of Roper on different forms of complex feedback. In this experiment 537 students were involved. The subject is instruction on theory of installation technology in the fields of sanitary technology, gas technology and heating technology. After a pilot test, two experiments took place. This study suggests that the application of complex feedback is effective, but does not significantly increase post-test results. Students with good reading comprehension skills benefit much more from complex feedback than those with poor reading skills.