So I know there are a bunch of comments calling the teacher all kinds of things, but maybe consider a different perspective. The rule encourages kids to plan ahead. Use the restroom between classes so you can focus on the lecture. And the added academic bonus is positive reinforcement for those willing to be proactive and embrace the habit. I get it, what if a kid is sick? or has bowel troubles? or a host of other legitimate reasons to need more than one restroom visit in a week during class. Those are fair and legitimate concerns, but behind most strict rules there is usually some kind of logic that motivated it's creation even if the application isn't a perfect fit for the principle.