Because of course assessing student work and making out lesson plans takes absolutely no time at all.
Classroom time is important, but an effective teacher ends up spending at least one hour outside the classroom preparing for what happens inside the classroom.
Of course, the Chicago Public schools aren't really composed of effective teachers based on their NAEP results.
Why did I know you were going to make another jab about the teachers rather than admit that your idea of them having only a 30-hour work week was ludicrous nonsense.
I'll grant that many school districts fail miserably when it comes to hiring good teachers, but the solution to that problem is not to make the pay worse so that only bad teachers are willing to take the job. This is not the 1950's krazen. Educated females have far more options in employment than teaching and nursing, so there is no longer a pool of competent cheap labor for those professions.