This study presents the case of development and evaluation of a STEM-oriented 30-h robotics course for junior high school students (n = 32). Class activities were designed according to the P3 Task Taxonomy, which included: (1) practice-basic closed-ended tasks and exercises; (2) problem solving--small-scale open-ended assignments in which the learner can choose the solution method or arrive at different answers; and (3) project-based learning--open-ended challenging tasks. The research aimed at exploring students' working patterns, achievements in learning the course, and the impact of this experience on students' motivation to learn STEM subjects. Evaluation tools included a final exam on factual, procedural and conceptual knowledge in the STEM subject learned in the course, class observations, interviews with the students, and administrating an attitude questionnaire before and after the course. Since the experimental class was quite heterogenic in regard to students' prior learning achievements and motivation to learn, some of the students completed just the basic exercises, others coped well with the problem-solving tasks, and only a few took it upon themselves to carry out a complex project. However, all students showed high motivation to learn robotics and STEM subjects. In summary, robotics provides a very rich and attractive learning environment for STEM education. Yet, the realization of this potential depends largely on careful design of the course methodology and especially the students' assignments in the class. One should recognize that often only some students are capable of learning a new subject on their own through project work, and these students also need to gain additional knowledge and skills before dealing with complex projects.