In the 18 states with no reporting requirements, cases can go unnoticed, such as the 2010 sexual assault of a girl in a Muncie, Indiana, high school bathroom, which resulted in a boy's guilty plea.
AP compared state education agency information from fall 2011 to spring 2015—across the four academic years for which most reported—counting only the most severe forms of sexual assault, such as rape, sodomy, forced oral sex, penetration with an object or unwanted fondling.
But 32 states and the District of Columbia do maintain information, though it is inconsistent and sometimes incomplete, The Associated Press found.
Some states required school districts to log any student sexual assault on school property or at school-sponsored events, but others required reporting of only those assaults resulting in certain types of student discipline.
For states with no education data, AP looked to the National Incident-Based Reporting System, a database of participating states' crime reports collected by the FBI.