Sexual assault on college campuses has made headlines for years, but The Associated Press sought to determine whether it also is a problem among younger students and, if so, to what extent.

There are no federal requirements for elementary and secondary schools to report such assaults and academic research aimed at quantifying the number of assaults at schools throughout the U.S. has been based only on sample surveys.

The AP sent queries to public education departments in every state and the District of Columbia for all available years of statistics on sexual assaults by students. Ultimately, A...