The aim of this study is to investigate the impact of online peer feedback in the Information Technologies and Software course on the improvement of collaborative problem-solving skills (CPS), which are considered essential skills for the 21st century. The impact of peer feedback on CPS was designed using a mixed-methods approach that combines quantitative and qualitative data in the research. The study employed a set of CPS tasks that were specifically designed to measure the target behaviors outlined in the 6th-grade Information Technologies and Software course curriculum. Additionally, the study made use of various instruments, including a peer feedback survey, a longitudinal rating scale for tracking the development of CPS, and a peer feedback interview protocol. As a result, a statistically significant difference was found between the CPS of the experimental and control groups. According to the results of the study, it can be expressed that the CPS and peer feedback skills of the students in the experimental group have improved and that they have a more positive attitude toward giving peer feedback and solving collaborative problems based on the results of the interview form. [This study was presented as a paper at CMEEP 2022 8th International Congress on Measurement and Evaluation in Education and Psychology.]