Many educational reforms highlight the need for collaboration, understood not only as a competence to be learned but also as a way of learning and teaching. Two types of collaboration can be found in classrooms: peer collaboration and teacher collaboration. The first focuses on how the teacher restructures interactions between pupils organized in pairs or groups. This permits cooperative learning practices, either by peer tutoring or through systems of cooperative learning. By implementing peer collaboration, the teacher is able to develop a new and transformative role which facilitates functions such as continuous assessment or immediate personalized attention, which are more difficult to carry out in environments where a traditional teaching approach is used. However, both the organization of the classroom for peer collaboration and this new teaching role require teacher training. Experiential learning is a key aspect of the training. Different levels of teacher collaboration exist, but the most complete is co-teaching: two teachers planning, implementing, and assessing the same lesson for a group of students. Co–teaching allows teachers to attend to the individual needs of their students; that is why it is such an important tool in inclusive education. Furthermore, it is a learning tool for teachers. Co-teachers can foster mutual observation, reflection, and planning of innovative practices, making working together a form of professional development. However, to ensure that pupils receive better attention and that teachers learn from each other, there has to be teacher training, and again, it must be addressed from an experimental perspective.