Debugging code is a central skill for students but also a considerable challenge when learning to program: helplessness and, in consequence, frustration when confronted with errors is a common phenomenon in the K12 classroom. Debugging is distinct from general programming abilities, therefore it should be taught explicitly. Despite this, debugging is an underrepresented topic in the classroom as well as in computer science education research, as only few studies, materials and concepts discuss the explicit teaching of debugging. Consequently, novices are often left on their own in developing debugging skills. This paper analyses the effectiveness of explicitly teaching a systematic debugging process, especially with regard to the students' self-efficacy and the resulting debugging performance. To this end, we developed an intervention, piloted it and then examined it in a pre-post-control-group-test-design: Both experimental and control groups were surveyed using a questionnaire and given debugging exercises as a pre-test. Afterward, the intervention was carried out in the experimental group, while the control group continued to work on debugging exercises. During the post-test, the students once more worked on debugging exercises and were surveyed. The results show a significant increase in both self-efficacy expectations and debugging performance in the experimental group in contrast to the control group. Therefore, our study provides empirical arguments for explicitly teaching debugging and simultaneously offers a hands-on approach for the classroom.