Your numbers are wrong. Most teachers teach 6 or 7 periods a day, with 42 minutes for planning. Above the elementary level, teachers see up to 170 students per day. I teach middle school and see almost every student in the grade, 162 students. There is grading to be done in that 42 minutes as well. If I grade just two assignments per week, and spend only one minute per student’s work (which is laughable), that’s already over five hours of grading a week. I only get 3.5 hours of planning time per week. But we haven’t even gotten to lesson planning or all the other administrative tasks yet.