Small class (3-4 years old): born between 2013.9.1-2014.8.31,children of employees in the on-the-job establishment of Peking University Headquarters, full-time postdoctoral children and children of three generations of employees. Among them, the third generation children of Peking University give priority to children with Haidian household registration, and their household registration address is the same as that of their grandparents. Kindergarten (2.5-3 years old): School-age children born between 2014.9.1-2015.2.28 are employed by Peking University Headquarters. Middle and large classes (4-6 years old): individual transfer places, school-age children of on-the-job career staff, and full-time postdoctoral staff of Peking University Headquarters.