This paper describes and discusses the design rationales of a system called My-Pet-Our-Pet that intends to realize an approach to using simulated animal companions to encourage students to help each other learn. A class of students is divided into several teams. Every student keeps her own individual animal companion, called My-Pet. An important component of animal companion is the student model of its master that supports self-reflection in different perspectives. Also, every team has a team animal companion, called Our-Pet, being kept by all the members of the team collaboratively. Our-Pet has a collective student model composed by all the student models of the team members. The design of Our-Pet help set a team goal through participating a competition game among Our-Pets of different teams, support collective reflections among team members, and shed light for the team how to help each other. We are currently conducting an experimental trail of the system in an elementary school where every student in the class has a Tablet PC.