Most of Wales's top-performing primaries are small schools with 100 or fewer pupils, according to a TES Cymru survey.
Small schools made up 63 per cent of the primaries and juniors at which all 11-year-old pupils achieved the standard expected for their age in EnglishWelsh, maths and science (the core subject indicator or CSI) in 2005.
Faith schools, some of them also small schools, made up a fifth of the top 86 performers. However, faith schools in Wales generally have better-off pupils.
Free school meal (FSM) entitlement was below the Welsh average of 19.7 per cent of pupils in nearly two-thirds of denominational primary, infant and junior schools for which figures were available in 2005.
In comparison, small schools for which FSM figures were available were spread fairly evenly across the full range of entitlement, with just over half above the Welsh average and just under half below it.
Supporters of small schools seized on the findings as further proof of their educational value.
Rural and small schools are considered more vulnerable to closure as pupil numbers continue to fall in Wales. Some authorities, such as Ceredigion, are also under pressure from external agencies like Estyn to reduce the number of small schools, because they are "extremely expensive" and an inefficient use of resources.
But Mervyn Benford, information officer for the National Association for Small Schools, said there was growing evidence about the efficacy of small-scale education - and that maintaining small schools can cost less than bussing pupils to bigger primaries.
He also dismissed claims that pupils in small schools benefit from smaller teaching groups. English inspection agency Ofsted believes the evidence for class sizes making a difference is inconclusive, he added.
"It is because small schools are closer to the family, and closer to the home and the local community," said Mr Benford, a former Ofsted inspector who has also inspected schools for Estyn.
"That relationship with the home makes it more likely that the home will work with the school, will share its values and standards, and will encourage children to take part in the process. It's the human scale factor."
He added: "Small schools succeed not because of smaller classes but because they are closest to the one education model we know works - the family model."
David Reynolds, professor of education at Plymouth university who lives in Wales, said the results paralleled findings in England about the academic success of small and rural schools.
But in England a small school is defined as 150-225 pupils, compared with a Welsh average of 172 and a higher proportion of much smaller schools (nearly 30 per cent with 100 or fewer pupils).
This means higher per-pupil costs of pound;5-6,000 or more in Wales, he said.
"These figures are not picking up small as better in Wales, but very small as better. And the very small schools in Wales will be much more expensive than average," he said.
Anna Brychan, director of the National Association of Head Teachers Cymru said: "The only valid consideration in deciding the future of small schools is whether they are serving the best interests of their pupils and communities.
"These results show that small schools in Wales are emphatically doing just that. It is testimony too to the huge dedication of staff and parents who are often working in difficult circumstances in terms of staffing and resources."
The key stage 2 figures, especially for small schools, need to be treated with caution as just one or two pupils can make a huge difference to the overall achievement of a small cohort of Year 6 pupils. In 2005, one primary saw its results shoot up to 100 per cent on the CSI, from 58 the previous year.
But for Margaret Cornell, head of 69-pupil Beguildy primary school near Knighton, Powys, what matters is not size but giving support to individual pupils.
Staff try to make every penny count, for example by bagging free paint and materials from national companies and collecting end-of-line wallpaper from DIY stores to sell on to raise cash that can be spent on learning.
"It's nothing to do with small schools, it's to do with targeting the pupils' needs," she said.
"When they start here, the children don't do well on baseline assessments.
These children get one-to-one support. The magic ingredient is learning support assistants, five over three classes."
The results at the Church in Wales primary speak for themselves: all Year 6 pupils achieved the expected standard in the core subjects in the three years to 2005, despite above average free school meal levels. But results went down this summer because two out of seven 11-year-olds hadJspecial educational needs.