The US Sanders and Rivers study still has legs and is often referenced
An extensive and highly influential 1996 US study in Tennessee, by William Sanders and June Rivers , found, interalia, that ‘ Differences in student achievement of fifty percentile points were observed as a result of teacher sequence after only three years.’
‘The effects on student achievement are both additive and cumulative with little evidence of compensatory effects.’ ‘Groups of students with comparable abilities and initial achievement levels may have vastly different outcomes as a result of the sequence of teachers to which they are assigned’. ‘Regardless of initial achievement level teachers in the top quintile facilitated desirable academic progress in all students’ …Whereas, ‘regardless of their entering achievement levels students under the tutelage of teachers in the bottom quintile made unsatisfactory gains’…
In short, ‘The single most dominant factor affecting student academic gain is teacher effect’ Bad teachers do retard the academic development of students. Its hardly rocket science , but the days when you state the ‘obvious’ without reference to evidence are long gone.
Cumulative and Residual effects of Teachers on future student academic achievement