One of the Welsh government's flagship education policies still "varies considerably" between schools three years after it was introduced.
The Foundation Phase for primary pupils - which involves learning through play - is having a positive impact on how pupils learn, according to a review.
But there are also concerns it doesn't prepare children adequately for yearly exams later in education.
Education minister Huw Lewis welcomed the findings.
Seen as one of the jewels in the crown of the Welsh government's education policies, the Foundation Phase has seen mixed success since its full introduction in 2011.
The scheme focuses on children aged three to seven and emphasises "learning by doing," aiming to encourage children to find different ways to solve problems.
A series of reports by Cardiff University researchers for the Welsh government to see how successful the scheme has been, said "overall, the practitioners/key stakeholders interviewed and surveyed reported that the Foundation Phase was having a positive impact on children and learning".
The research was based on class observations, interviews with teachers and pupil surveys, as well as feedback from others.
'Lessons to be learned'
There were concerns about how the programme prepares Wales' three to seven-year-olds for annual tests they face later in school.
There were also worries that the high numbers of teachers needed for the scheme works against nurturing independent learning.
- Practice "varied considerably across classes, year groups, schools and areas of learning"
- Some people thought "children were becoming overly-dependent on high adult:child ratios"
- Boys, children with special educational needs and children with English or Welsh as an additional language were reported to benefit the most
- Overall parent/carer satisfaction with their children's education was high
Mr Lewis said the reports were "good news for young people in Wales".
He added: "There are lessons to be learned.
"The reports do tell us that we need to do more to ensure a consistent experience for all learners across Wales.
"At present there is too much variation for learners from class-to class and from school to school. This must stop.
"Consistency is key if we're to deliver the same positive outcomes for our learners."
The reports were commissioned in 2011 and Cardiff University and the WISERD (Wales Institute of Social and Economic Research, Data and Methods) research centre are evaluating the long-term impact of the scheme.