James Pankiewicz comments

Kneeling in seiza for 20 mins or more is perfectly normal in many situations. If you are not used to it its uncomfortable but it doesn't cause injury. The upright sitting position tends to make you awake and aware, hence a good position to meditate or do active recovery between exercises. If a teacher in a martial arts dojo had the students sit in seiza for 20 mins while explaining or demonstrating something there would be no outcry. Its expected. So while it may have been out of the ordinary for this teacher to have these students sit in seiza in this location, its hardly equivalent to corporal punishment or physical abuse. Dial it down, people. A generation ago, this kind of outrage would have seemed entirely ridiculous - and thats not because somehow our elders all thought physical abuse of minors was acceptable. They didn't. But sometimes you have to be out of your comfort zone to learn a lesson.