Funding targeted at improving the educational attainment of the most deprived children is a "life-saver", say headteachers.
More than 600 schools across Wales have received cash from the pound;16 million Raise (raising attainment and individual standards in education) fund, and have started implementing support projects.
Critics say needy pupils in other schools have missed out because the Assembly government used free school meal entitlement figures to allocate the cash.
But the scheme has been defended by David Egan, special adviser to education, lifelong learning and skills minister Jane Davidson. And participating heads say their pupils are reaping the benefits.
Nantymoel is a former mining village in the Ogmore Valley, north of Bridgend, which suffers from a lack of jobs, older terraced housing and an ageing population.
Geoff Roberts is the head of the village primary which is grappling with falling rolls. Three in 10 of the pupils are classed as having some sort of special need, and 27 per cent get free school meals.
"This is not an affluent community and many of the kids come from a background of economic and social disadvantage," he said.
The school has been allocated pound;14,000 under Raise and has decided to target the money at six pupils in Year 3 and another six in Year 4 who need additional support.
A classroom assistant is now employed to work with these two groups each morning, providing help with reading, writing and maths. "These are all children who are not reaching the attainment levels they should be," said Mr Roberts.
"But by raising their standards, we will also have a knock-on effect on the rest of the school."
Mrs Margaret Chantrell, head of Holyhead high school, Gwynedd, called Raise a "life-saver". "It has given us funds to do the things that we always wanted to do," she said. The school is spending its pound;70,000 Raise cash on improving standards in the core subjects of English and maths. It has also set up boy-specific schemes to try and close the gap between their attainment and that of girls, and tried to address behaviour issues.
Professor Egan defended the way in which schools have been selected for extra help via Raise to tackle low attainment.
Speaking at a seminar on educational disadvantage and low attainment, organised by Cardiff university's school of social sciences, he said: "We were aware that free school meals are not always the best indicator of disadvantage, but we thought there was nothing more reliable."
The government decided to act when it became apparent that a gap was opening up between the performances of schools in Wales and England.
A report from inspection agency Estyn found that many schools lacked a strategy to improve the performance of the most disadvantaged pupils. And another from the charitable Rowntree Foundation found a widening gap between pupils from deprived backgrounds and the more advantaged.
Professor Egan said that against this context, it was felt that money already being put into the system to cater for disadvantage was being too thinly spread and it was hard to detect any impact.
He promised Raise would be stringently evaluated, and schools would be expected to provide evidence that the cash has been targeted at disadvantaged pupils.
"This is the biggest school improvement programme we have had in Wales. We will not get quick returns. We must build the capacity of the schools first," he added.
Dr Ruth Lupton, one of the other speakers at the Cardiff university seminar, said the educational attainment of children was affected by where they lived.
Schools in deprived areas lacking services and facilities had problems in recruiting and then retaining staff.
In one study, half of the teachers in a school were not qualified to teach their subject.
Teachers' actual performances are also adversely affected by the schools'
context. Teacher time was wasted on behaviour problems and on giving out and collecting books and equipment in each lesson because children did not have their own.
Teachers' expectations of the children and of themselves were lowered.
Dr Lupton, of London university's institute of education, added: "We need to look at core resources for such schools so that they can do their day-to-day work."