Final answer:
The school mass killing with the most fatalities AND injuries occurred at Kent State University on May 4, 1970, during an anti-Vietnam War protest.
Step-by-step explanation:
The school mass killing with the most fatalities AND injuries occurred at Kent State University on May 4, 1970, during an anti-Vietnam War protest. Soldiers of the National Guard fired into a crowd of campus protesters, killing four students and wounding nine. The event polarized the nation, with some referring to it as a 'riot' and others as a 'massacre.'