There would be few teachers - certainly none of any great merit - who would not concede that learning takes place best at a pace perfectly calibrated to the learner's needs. The ideal class size will always be one.
It has become a commonplace of educational discussion - in the public arena if not always in the academic research community - that smaller class sizes will ineluctably lead to improved outcomes. Negotiations between the Government and teacher unions have perennially focused on lowering teacher-pupil ratios. Attention has been devoted to getting more teachers in front of classes.
But the results of a new study by John Hattie, a Professor of Education at the University of Auckland, give the lie to the conventional wisdom. Hattie's 15-year study - technically known as a meta-analysis since it synthesises the results of 50,000 previous studies of more than 80 million students worldwide - is thought to be the largest-ever overview of student achievement. And in ranking the factors that contributed most to the quality of children's education,
it found that class size was far from the most important. Furthermore, other criteria popularly cited as predictive of educational attainment - the type and decile rating of the school attended; whether or how much homework was done; and students' dietary or exercise habits - did not emerge as being of major importance.
The results overwhelmingly indicated that the key to effective teaching was the students' interaction with teachers and in particular the quality of feedback students received.
This will come as no surprise to anyone who has ever sat in a classroom. We can all remember teachers who had a profound impact on our lives because of the quality - not necessarily the quantity - of the attention they gave us. Important lessons that they taught us remain deeply etched in our memories.
But if Hattie's findings rhyme with commonsense experience, they have far-reaching implications for public policy and educational funding. As he says, they point to the need for spending to be targeted to teacher salaries - and, more controversially, they suggest that we should move towards a system of performance-related pay for teachers.
It's an idea that could restore the lustre of a profession held in insufficient regard here but seen in many countries as on a par with medicine or the law. But it is a suggestion unlikely to find favour with teacher unions who have, in contract negotiations, sometimes displayed more concern for their membership than their charges.
One union leader has already said performance-related pay would be "extraordinarily problematic". But logistical difficulties should not stand in the way of moving towards such incentives, which could improve the recruitment and retention of excellent teachers who are lured away from education because they can earn more elsewhere. As it stands, teachers must step out of the classroom and seek positions of responsibility if they want to increase their earnings. Yet good teachers who want to remain good teachers should be treasured and rewarded appropriately.
Hattie is widely respected internationally as a top-flight quantitative educational researcher. But his findings still need to be read with caution. The thorny question of socio-economic status will have been addressed in his project's constituent studies - but inevitably this control will have been exercised variably because the results are diverse and international.
The correlation between schools' decile ratings and educational results here cannot be ignored as policymakers explore a way forward. It may be that we should provide salary incentives to attract good teachers to schools where they do not typically seek to work. If this research is to lead to any meaningful change it will be to improve the calibre of teachers in all schools, and not just in the ones that can afford them.