Conflict between Class Work and Home Work.
On a normal working day, school hours may last between 6 and 8 hours. And after that, when they're back home, they normally stay up late to attend and finish all the house chores. Just imagine after a hard day's work at school, they're further obliged into family and personal commitments / responsibilities, which is as equal or may be more valuable than the others perhaps.
Most often than not, it gets really down on them. In addition, they've got to prepare for future lessons and spend time in grading papers. They may have to answer calls from parents for any urgent issues and genuine reasons, during their 'private' times even.
Teacher's role is usually a dilemma, if it is not managed properly.
Non-teachers may not be able to fully comprehend the tension, except for teachers themselves.