The experiment was conducted in a rural county (LH County) of Hunan Province in central China for five months, from September 2015 to January 2016. The duration of the experiment covered the entire autumn semester of the academic year 2015/2016. With the permission
and cooperation of the local education bureau, we randomly selected five elementary schools from the complete set of elementary schools in the county to conduct the experiment. Students from the participating schools were initially randomly assigned to different classes at the start of the first grade. We focused on students in the third, fourth, and fifth grades. We randomly chose two classes in each grade from each school. By lottery, one class was assigned as a treatment class in which we randomly formed teams; the other class was
assigned as the control class in which no intervention was implemented. We requested the students fill out a paper-based questionnaire twice during the experiment. The first-round questionnaire was given two weeks prior to the start of the autumn semester, and the second round was conducted two weeks before the final examination. The questionnaire collected information about the students’ demographics, attitudes toward study, and measurements of personality traits. The questionnaire also gathered basic information about their parents, such as education, occupation, and income.The students filled out the questionnaires during self-study sessions in the presence of head teachers, who then collected the forms and uploaded detailed information to our online system. To guarantee data accuracy and completeness, the head teachers returned incomplete forms or forms with obvious errors to the corresponding students for amendment until the forms were satisfactory. We supervised the entire procedure of questionnaire completion and uploading to ensure the accuracy and effectiveness of information. Team size was set at five to six members. To be comparable with current classroom structure, We first assigned students to three sets according to height, that is, below average, average, and above average height. Within each set, every six students were grouped by lottery, and their seats were also assigned by lottery. We ensured that shorter students took front rows, which is how they would be assigned if they were in the control classes. We also ensured that members of a same team sat next to each other either in the same row or in the same column. In consideration of the children’s visual development, seating was shuffled every two weeks, but the team members remained unchanged. We picked up some prior school activities as team tasks to increase interaction within teams and raise team awareness.