Sutton Trust research by Oxford University found that poorer children have less chance of taking the A level subjects that the top universities favour because of a lack of support at home.
But if mums and dads put in the effort to give their children the experience of 'academic enrichment activities' at home from the age of 11 - including going on trips to museums and galleries, and reading for pleasure - their chances of gaining good A-level results are significantly improved.
And when they get into the habit of daily homework, students are nine times as likely to get three A-levels.
The study, Subject to Background by Professor Pam Sammons, Dr Katalin Toth and Professor Kathy Sylva, from the Oxford University Department of Education, looked at the experiences of more than 3,000 young people from the age of three for the Effective Pre-School, Primary and Secondary Education (EPPSE) project.
They found that only 33 per cent of bright but disadvantaged students took one or more A-level exams in 'facilitating subjects' that universities prioritise, such as Maths, English, the sciences, humanities or modern languages, compared with 58 per cent of their more advantaged counterparts.
At the same time, only 35 per cent of the disadvantaged group – identified as able from their test scores at age 11 – went on to get three A-levels in any subjects compared with 60 per cent of their bright advantaged peers.
But the researchers identified a number of factors that made it significantly more likely that the bright disadvantaged students would attain three A-levels including:
· Having benefited from pre-school education, especially of higher quality;
· Having had enrichment and supportive home learning environments from a young age, including reading books and going on educational outings during the early years of secondary school;
· Having been to an outstanding secondary school (as rated by Ofsted) and one where there were good relationships of trust between teachers and students, with regular feedback;
· Having spent more time doing daily homework on a regular basis before and during their GCSEs.
Sir Peter Lampl, chairman of the Sutton Trust and of the Education Endowment Foundation, said: "The fact that bright disadvantaged students fall so far behind when they reach their A-levels shows that government and schools urgently need to do more to support able students from less advantaged homes.
"We must ensure that access to the best schools and opportunities for academic enrichment outside school are available to all students. It is also vital that schools advise their students on the right subject choices at GCSE and A-level so as to maximise their potential."
Professor Pam Sammons, co-author of the report, said: "There is no silver bullet that alone can make a difference but a combination of good schools and pre-schools, the right home learning environment and supportive teachers ready to monitor progress and provide good feedback can all ensure that bright but disadvantaged students get the chance of a good university education.
"There are important lessons here for teachers and policymakers seeking to reduce the equity gap in attainment."The report recommends that enrichment vouchers, perhaps funded through the pupil premium - additional funding for publicly funded schools in England to raise the attainment of disadvantaged pupils and close the gap between them and their peers - should be made available to encourage reading for pleasure, educational trips and out-of-school study for bright pupils.
It also said schools should provide more opportunities for able students to undertake academic enrichment activities where these are not available at home, including through structured 'gifted and talented' programmes, and monitor their progress more effectively.
They should also encourage them on the best subject choices, particularly for leading universities, with support from a strengthened careers service.
The report added that bright but disadvantaged students should have more opportunities to go to the best schools, and disadvantaged children should have access to good quality pre-school settings with qualified staff.
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