What characterizes "hard-to-staff" schools, those schools that have difficulty in finding and retaining qualified, effective teachers? Many are high-poverty inner-city schools or rural schools that, as a consequence of their location in economically depressed or isolated districts, offer lower salaries.
Are teacher salaries lower in low-income school districts? As in the context of this quote, are the low salaries a reason why low-income school districts are harder to staff with effective teachers? Any numbers to show this?