A study by academics from Toronto University, due to be released in the next few weeks, found widespread support in schools for "the most ambitious education reform in the world". But the team, led by Professor Michael Fullan, acknowledged that the primary curriculum had narrowed and revealed widespread teaching to the test.
The second in the Government-commissioned series of three annual reports was presented to ministers last week. It said there was less variability between schools' ability to teach children at least a minimum level of reading and writing than before the strategy was introduced. Teachers also had a growing sense of competence and confidence, and all staff were highly motivated to focus on literacy.
But researchers, who had open access to schools, local authorities and ministers' meetings, found that teachers were concentrating on assessment rather than improving reading.
Lorna Earl, one of the Toronto team who presented the findings to the United Kingdom Reading Association, said: "We see a great deal of focus on getting children ready for the assessment, particularly in Year 6."
The report said improvements in national test results had come about because of the focus on literacy, more targeted objectives, training and monitoring. However, Ms Earl said the strategy had yet to push the limits to "deep learning" where children were involved in self-monitoring and could think and learn for themselves.
Teacher shortages were pinpointed as a potential threat to schools' ability to build on their initial successes.
"Staffing and continuity is a serious problem," said Ms Earl. "The only way the strategy will become embedded and continue is if schools have the capacity to self-review their own learning. We need to work out how we bring people into the profession and keep them there." The study also discovered that other subjects had been neglected because of the demands of the strategy. "Subjects that have not been the focus of Government initiatives have suffered - we got that message regularly."
Since the strategy was introduced in 1998, key stage 2 results have risen each year. The report found the gap between higher and lower-ability children was closing.