Use of mobile devices and widespread adoption of wireless networks have enabled the emergence of Ubiquitous Computing. Application of this technology to improving education strategies gave rise to Ubiquitous e-Learning, also known as Ubiquitous Learning. There are several approaches to organizing ubiquitous learning environments, but most of them employ a centralized architecture. This approach offers some benefits, such as facilitating access to learners' profiles, but it also involves certain disadvantages intrinsic to centralization, such as scalability concerns. This article presents CoolEdu, a collaborative model for decentralized ubiquitous learning environments. CoolEdu improves the learning process by stimulating interaction between learners. It employs an agent-based approach and a socio-interactionist model based on the "collaboration with more capable peers" concept introduced by Vygotsky. The model was implemented and applied in two practical experiments. Firstly, CoolEdu was integrated with an infrastructure used to create ubiquitous learning environments. The resulting environment was evaluated in a simulated scenario designed to explore CoolEdu's functionalities. A second experiment was conducted with 25 volunteers to evaluate the quality of forming collaborative peer pairs based on Vygotsky's theory. The results were encouraging and demonstrate the potential for application of CoolEdu in real situations.