Context: Comparative study of software development methodologies in millenials high school students. Objective: This paper compares the performance and satisfaction of both students and teachers in using two development strategies in a K-12 Computer Science teaching practice. Method: This study includes an experiment, administered in a laboratory controlled setting to measure students' performances. Results: Scrum produces less usable software with better working features compared to Waterfall, it is also more appreciated by students. Teachers are more experienced with Waterfall, which also offers more control on the development process. Conclusions: From an educational perspective, the two methods are equivalent. Since we noted an overall positive effect on the learning environment, we recommend that at least one method be taught in practice.