What really works in schools and classrooms? How much difference can homework and class size make to a child's ability? Sarah Montague interviews John Hattie, Professor of Education at the University of Melbourne and Chair of the Australian Institute of Teaching and School Leadership. Over 20 years, he carried out one of the biggest pieces of education research, compiling studies from previous decades and comparing the effect they have on attainment and ability. His work is ongoing, but the results show a league table of effectiveness. It reinforces things you might expect, such as the importance of teachers, but also offers some surprises that might have parents and teachers questioning their priorities. Presenter: Sarah Montague Producer: Joel Moors.