All data indicates that teachers are working less than 40 hours a week on average, which makes me believe that the ones putting in 50+ hours are a vocal, tiny minority.
I have the impression (from my wife and her coworkers) that it's much easier for elementary and middle school teachers to work the contracted hours and not bring their work home with them.
High school just comes with a lot of extra baggage too.
I've never understood why subjects and student age aren't considered in teacher pay scales across the board. My experience is limited, but I've never seen an instance where anything other than time and credentials (generally degrees) were considered.
"Union contracts generally mandate that gym teachers must be paid the same as calculus teachers, with the predictable result of surpluses of gym teachers and shortages of calculus teachers."