Researchers from the Scottish Government-backed survey Growing Up in Scotland said high quality nursery education delivered by qualified staff was vital to improve children's vocabulary and problem-solving skills.
They also highlighted the importance of providing the additional free places at times of the day that were suitable for working families to ensure the maximum benefit.
All three and four-year-olds in Scotland receive a minimum of 475 hours of free pre-school education per year, but the entitlement will rise to 600 hours in August.
The policy has been designed to help working families as well as being part of a wider commitment to ensure children get the best educational start in life - particularly those from deprived backgrounds. But there have been concerns over the quality of some nurseries, fuelled by the decline in qualified nursery teachers.
In addition, some families have been unable to access the places as many council-run nurseries do not offer the extended hours they require to cover the working day.
A report by researchers from the Growing Up in Scotland project concluded: "The findings here suggest the imminent increase in pre-school entitlement due in August is unlikely to have either a direct positive or detrimental impact on child outcomes.
"There may be some benefits from the increase in statutory pre-school hours through increased opportunities for both parents to work or to pursue further and higher education.
"However, the increased hours of entitlement alone are limited in allowing parents to take up work and education opportunities."
Teaching unions used the report to highlight the importance of qualified teachers in the delivery of quality nursery education.
A spokesman for the Educational Institute of Scotland (EIS) said: "We continue to firmly believe, and the weight of evidence continues to demonstrate, that the proper involvement of fully qualified teachers in all nursery settings is the best way to ensure a high-quality nursery education experience for all young children."
Eileen Prior, executive director of the Scottish Parent Teacher Council, stressed the importance of nurseries offering hours that suited working families. She said: "A significant factor for parents is the way in which pre-school hours are delivered and how it can be flexible to meet their needs."
A Scottish Government spokeswoman said the report proved the vital importance of pre-school education. She said: "The report adds to the growing evidence of the positive impact that quality pre-school provision can have on children and their families and also shows that children from both low and high income families benefit equally.The finding that the level of care and support given to children... significantly enhances their cognitive development, is one which we welcome."
Figures from the Growing Up in Scotland survey show children who attend the best nurseries can see significant improvements in their vocabulary and problem-solving skills.
Interestingly, the report found the quality of care and support children receive in pre-school education had the single biggest impact on their progress.
But it also stressed the importance of the level of qualifications of nursery staff on the educational benefits experienced by children.
The survey also found that state-run nurseries were generally of a higher quality than those in the private sector.
Growing Up in Scotland is a major longitudinal research study tracking the lives of thousands of children and their families from the early years, through childhood and beyond. The survey is funded by the Scottish Government and the results are used to develop policies and services for children and their families.