Pop-psychology. What was this principal thinking?
When you unhinge the social sciences from God this is the result.
“To educate a man in mind and not in morals is to educate a menace to society.” - T. Roosevelt
Something along the lines of "If this is handled in the school, there won't be any bad publicity".
If the police are never notified, there is no crime. There is no scrutiny. There are no questions.
Sure, a student here or there may be crippled physically and mentally for life. But that's all secondary to the amount of paperwork the principal would have to fill out if the authorities were called. Certainly, you can see the dilemma. /s/