I made a little picture of the allocation of teacher hours in poor versus wealthier schools, taking data from the most recent School and Staffing survey tables.
Teachers in schools with most students on free or reduced-price lunch spend an extra 1.7 hours per week delivering instruction when compared to teachers in schools with teachers at wealthier schools. The teachers at the poorer schools spend 2.2 hours less on all other activities. (This includes the time spent weekends and evenings prepping, grading, and so forth.)
The differences in time allocation strike me as notable. Since there are relatively more inexperienced teachers in poorer schools, I would have thought that teachers in these schools would be putting in considerably more time on lesson plans and such.
It’s not obvious what the optimal allocation of teacher time is, but the differences are large enough to be worth thinking about.