We constructed a science class where Japanese university freshmen experienced scientific activities. The class topic was the psychology of discovery. Students discovered laws and regularities of phenomena through experiments and constructed explanations why the phenomena appeared. Generally, students face many difficulties in constructing an explanation in student-centered learning. First we identified the factors that interrupt the students' construction of explanation through the review of preceding studies and our empirical investigation. Then we designed the class in which the students collaboratively construct the explanation by using the jigsaw method for overcoming these difficulties. As a result, almost all students successfully constructed the explanation. In the students' collaborative activities, we observed the students' monitoring other members' explanation and referring to knowledge that other members acquired. These collaborative activities have the students overcome the difficulties, leading to successful construction of explanation. As our conclusion, we propose the following design principle for collaborative learning: constructing a jigsaw group where knowledge needed for explanation is distributed to each of the group members with understandings on the structure of explanation based on task analysis, and having students collaboratively engage in constructing explanations.