During their school years, especially middle school and high school, students try to participate in extracurricular activities. Games and practice leave little time and energy for students to do homework. Many of them have the "team" mind-frame and tend to put sports and or clubs as their first priorities. Having homework, quizzes, and tests add tension to the students schedule. Test grades begin to drop due to lack of studying. http://http://stress.about.com/od/studentstress/a/school_anxiety_3.htm
According to http://http://www.stressfocus.com/stress_focus_article/teen-stress-causes.htm school is the major cause of stress, accounting for 78%.