Project-based learning is an active method that develops the maximum involvement and participation of students in the learning process. It requires the teacher to energize the learning scenario by promoting the cooperation of students to investigate, make decisions and respond to the challenges of the project. It also requires activating an evaluation system that promotes awareness, reflexivity and a critical spirit, facilitating deeper learning. This case study aims to understand the functioning of cooperative work established during the application of the method, as well as to know how the evaluation process progresses in the perspective of a group of teachers of secondary education that set up this methodology in their classes. The data obtained from interviews with the teachers involved in the study, teachers’ notebooks, and open-question questionnaire applied to high-school students are analyzed. Although the students were organized in small groups in order to develop their collaborative skills, intragroup frictions and conflicts were not sufficiently addressed or supervised in time by the teachers, thus resulting in an incomplete development of the synergies and collaboration necessaries to the project. From the point of view of the evaluation, the importance of the implementation of training and shared evaluation systems is well recognized, although a more traditional evaluation model, which does not sufficiently address the project development process prevails, and the value of the qualification on the final product achieved still weights.