First, a list of all counties in was obtained for the study regions, namely Shaanxi Province or Ningxia Autonomous Region. Second, study counties were randomly selected from those meeting the official criteria for impoverished counties. Third, a list of all primary schools in sample counties was created using official records. Fourth, researchers used official records and their own canvass survey to identify all schools with the following characteristics: (i) six grades (i.e., 'complete' primary schools, or wanxiao), (ii) boarding facilities, and (iii) 400 or more students. Fifth, primary schools were randomly selected from these sampling frames. Finally, only fourth grade students in sample schools were randomly selected for inclusion in the studies.