Short answer, yes.  The reason for this is complicated.  First, playing sports at school is a privilege, not a right, so the school district can require you to do certain things before they will allow you to join the team.  Second, mandatory drug tests to join a school's team have been upheld in court.  However, in a case called Verona School District v. Acton, the U.S. Supreme Court upheld a drug testing policy where the school had a serious problem with students using drugs, especially students on the sports teams.  Being forced to take a drug test is considered an invasion of privacy.  But, because playing sports for your school is not mandatory and the school has an interest in making sure that its athletes are not on drugs, your school can force you to take a drug test if you go out for sports.