I just looked at my class roster for this next school year. Two of my classes have 37 students in them. The other two have 31 and 30. I don't even have enough desks for that large number. I actually had a nightmare about it last night. I teach seventh grade and having 37 students in a class is a managing nightmare! We went from having three classes a day and a planning period to four classes a day and a planning period. Not only will we have less planning time this year, but more students.
I will have 135 students total. If I spend thirty seconds a day grading one paper per student, I still would not have enough time to get it all done and recorded during my 80 minute planning period. That doesn't take into consideration planning for instruction, making parental phone calls, and attending mandatory professional development during two planning periods a week. That gives me about four hours total a week to do all my grading, communicating, and planning.
I usually spend about fifteen additional hours a week working on school-related work. I arrive at school at 7AM and leave at 3:10 (to get my own kids from school). I get about fifteen minutes for lunch and am lucky to find time during the day to use the restroom. So, I put in about eleven hours a day.
I'm not trying to discourage someone from becoming a teacher, but don't want to sugar-coat it either. I really think the hours put in during the school year, the ridiculously large classes, the lack of administrative support, the difficult parents, and the apathy of students is what often drives teachers out of the profession.