Sir Peter Lampl writes about education reform in the Sunday Times.

Thursday’s school league tables revealed that in a quarter of English sixth forms and colleges not a single student achieved the A-level grades needed to go to one of our leading universities. Our research at the Sutton Trust shows there are five independent schools that get more places at Oxbridge than 2,000 state schools and colleges combined.

While the gap in GCSE results between pupils from the poorest homes — those entitled to free school meals — and other schoolchildren narrowed a little, the difference is still vast. Among white working-class boys, only 26% gain five good GCSEs, compared with a national average of 59%.

The government’s answer has been to create more academies — state-funded schools that are independent of local authorities. The best academies get excellent results and have improved more quickly than other schools. But too many academies were below the government’s minimum standard in last week’s tables. Rather than structures, the real focus needs to be on standards and more specifically on practical approaches to improving teaching. The quality of teaching is the single biggest factor that affects results in schools.

Research by the London School of Economics for the trust shows that English schools could move into the world’s top five education performers within a decade if the performance of the least effective 10% of teachers were brought up to the average.

Research at Harvard has shown that if you leave a low-value-added teacher in a school for 10 years, rather than replacing him or her with an average teacher, an average class of 28 pupils will lose a total of about $2.5m (£1.5m) in lifetime income.

Like many people from the business world, I used to have a negative view of teachers. The assumption is that they have an easy job with long holidays, early retirement and generous pensions. But after spending the past 15 years in education, chairing the trust and more recently the Education Endowment Foundation, my view has been transformed.

I now have nothing but admiration for teachers, particularly those in inner cities who are often working wonders against the odds. It should be nothing less than a national priority to find better ways of evaluating, developing and compensating them.

Too often, we are seduced by high-profile initiatives that distract us from what is really important in improving the standard of education. A lot of attention has been focused on those entering teaching and too little attention on improving the standards of the 440,000 teachers already in England’s classrooms.

Last week the trust and the Education Endowment Foundation launched an online guide for teachers that summarises the results of more than 5,000 pieces of research from around the world about what works in improving pupil achievement. Based on work by Durham University, it is constantly updated as additional research becomes available.

Some approaches popular with teachers appear far less effective than you might think. For example, there is very little proof that reducing class sizes by small amounts or employing extra teaching assistants — as currently deployed — improves learning. Yet both are practised extensively in schools.

By contrast, there are other approaches that are less expensive and deliver better results. The single most effective way to help children gain good results involves teachers giving their pupils better feedback. When teachers explain to pupils how they could improve their schoolwork and when pupils reveal to teachers what they know about a subject, such feedback is equivalent to the gain you would get by spending an extra eight months in the classroom, so long as teachers strike the right balance between encouragement and correction.

On the other hand, reducing class sizes has an average gain equivalent to three extra months, and has only really been shown to work well in classes with fewer than 17 pupils.

With schools having to manage their budgets more carefully, it is important for them to look at the approaches that will offer them good value for money as well as good results. The biggest gains come in getting teaching right. Yet it is surprising just how few schools look at the research before deciding how best to improve their results and prioritise the development of their most-prized assets: teachers.

That’s why the Education Endowment Foundation is running trials of different programmes in schools and using more than 10% of our £135m endowment from the government to evaluate them rigorously. Where programmes are proven to be cost-effective, we want to see them rolled out to many more schools.