The Campaign for Learning found that parental involvement in a child's education can mean the difference between an A* and an "also-ran" at GCSE.
The report, called Give your child a better chance, by Dr Leon Feinstein of the London School of Economics, said: "Interested parents made a huge difference, regardless of class or income.
"However, low education, low social class and low income are often associated with low parental interest.
"It is necessary to find ways of encouraging and supporting involvement, rather than simply blaming the parents."
The study has been released to coincide with Family Learning Weekend (October 10-12). It found that almost half of parents did not talk to teachers even once during a school term because many felt inadequate or lacked knowledge about the curriculum, and were fearful of "getting it wrong". Others had bad memories of their own school days which tainted their view of school and teachers.
The campaign wants more funding for courses and activities that support parents in their children's education, and more campaigning to promote the value of parental involvement.
Susie Parson, the campaign's chief executive, said: "For too long, parents in economically deprived areas have been judged insufficient. We believe that family learning is the most neglected area of current policy."
Meanwhile, a separate report found that young children were being turned into "robots" by schools desperate to improve their league-table ranking.
The survey of 2,000 mothers in England and Wales found that more than eight out of 10 thought that their children had too much homework, and an increase in the number of projects and exams was ruining home life and leading to arguments.
Sian Rees, editor of Real magazine, which carried out the childhood stress survey, said: "The stress being heaped on children from a young age is unbelievable.
"Schools are turning children into homework robots in a bid to get further up the league tables."