I had an actual part-time job working in grade schools through Americorps and Boy's and Girl's Club working with struggling math and reading students. I was scheduled between 10-20 hours per week in the school working with kids from K-5.
I spent more time preparing for that job, creating activities to help students, and then actually going into the schools and working there than I spent working at my full time job after I graduated college. That was necessary in order to keep students engaged, make sure they stayed on pace with goals and to get enough material ready for all students in all grades. And I was only working with around 5 students at a time for 30 minute blocks.
Teachers have to do what I did and then multiply it by 5 or 6. You can look down on teachers all you want, you can disparage what they mean to not only the education of children, but to the community as a whole. But to consider their careers as nothing but a part-time job is one of the most insulting things I have ever heard.