The importance of feedback on students' learning activities, so as to facilitate high learning effectiveness, has been shown before. However, the effectiveness of feedback on students' learning activities, when students learn engineering processes based on computer based simulations, is much less well known. The purpose of this study is to analyze the impact of 'correcting feedback' (i.e. the feedback indicates only students' mistakes) and 'reflective feedback' (i.e. the feedback includes a hint to encourage the student to re-think a specific answer) on learning effectiveness of engineering students, when using computer based simulation in order to enhance the learning of engineering processes. The impact of 'reflective feedback' is analyzed by carrying out semi-quasi experiments using experimental and control groups of students. It is found that 'reflective feedback' does not result in higher learning effectiveness and that the students of this study prefer to correct their mistakes by focusing on 'correcting feedback' and previously learned content, while using a 'trial and error mentality'. The results provide evidence, first, about the impact of students' learning background when using teaching simulators, and, secondly, that simulators showing both, 'correcting feedback' and 'reflective feedback', may reduce the stimulating effect of 'reflective feedback' because of the presence of 'correcting feedback'. Consideration of these findings will contribute to further improvement of process teaching simulators. This study is part of an ongoing research effort related to computer simulation based learning in engineering education.