Compulsory one-to-one tuition to boost literacy among struggling pupils, which was axed by the Coalition, "significantly improved" reading and writing skills, according to Government-commissioned research.
The study, commissioned by the Department for Education, also showed that schools which used early intervention to raise literacy standards had "significantly better" test results in reading and writing at key stage 1.
The research, undertaken by the Institute for Fiscal Studies (IFS) in collaboration with the National Centre for Social Research, assessed the impact of the Every Child a Reader programme, which targeted low-attaining six and seven-year-olds.
Schools can still run the initiative, but dedicated funding for it has been removed, sparking criticism that its use will become a "lottery".
According to the research, in schools using the programme the proportion of pupils reaching their expected level in reading and writing was 2 per cent higher than in similar schools which had not used the scheme.
The study even claims pupils who took part could expect to earn an additional #163;6,000 over their lifetime if their improvement in attainment lasted.
But IFS senior research economist Haroon Chowdry said the scheme, which costs around #163;3,000 per child in the first year and #163;2,600 per child thereafter, is expensive.
"Every Child a Reader seems to have a substantial effect on the lowest-performing seven-year-olds, especially boys," Mr Chowdry said.
"(But) in the tightest public spending environment for decades, the key question is whether policies represent good value for money."
The last Labour government pledged that, by 2011, all children falling behind in literacy would receive either one-to-one or small-group tuition.
But last year, education secretary Michael Gove removed the ringfencing around the funding, saying he wanted to increase heads' budgetary freedom.
Shadow education secretary Andy Burnham slammed the decision, saying tuition would now be a "lottery".
Russell Hobby, general secretary of heads' union the NAHT, said the cost should not be a bar to Government support.
"This is one of those things you can't afford not to run," he said. "It was extremely well liked by those that used it ... It's almost as if you can see the progress take place in front of your eyes," Mr Hobby said.
A DfE spokesman said: "Every Child a Reader is still up and running. The money is still going to schools; we are simply untying heads' hands."
THE HEAD'S VERDICT
After using Every Child a Reader for four years, Mike Welsh, head of Goddard Primary in Swindon, believes the Government should support it, despite the expense.
"We have seen excellent progress in getting children to their appropriate reading age."
Mr Welsh added: "While one-to-one tuition can be expensive - not intervening in a six-year-old's reading ability will be far more costly for the system as a whole further down the line."