In a report out this week, it concludes that developing consistency in teaching and seeing pupils do well generates the most job satisfaction, enhanced by the induction and EPD programme.
Other influences encouraging the feel-good factor among new recruits include a reduced timetable in induction year, extra time for planning, sharing classroom experiences with other teachers and contributing to whole-school initiatives, according to Estyn.
However, there are concerns that EPD has not been so successful in supporting a few new primary teachers without permanent posts to stay in the profession.
"Financial insecurity often forces these teachers to consider leaving the profession. This is a substantial waste of their talents and the costs of training them."
Neil Foden, head of Friar's School in Bangor. said the standard of NQTs was improving. But he claimed current EPD funding did not allow for extensive professional development.
"A commercial course could cost 30 per cent of available funding and you may not get more than five days' supply for pound;1,000. Better schools funding gets tighter every year so there is no real prospect of adding to EPD."
The report, Induction and Early Professional Development Programme on Teacher's Job Satisfaction and Retention, says teachers registered with the General Teaching Council for Wales has shot up from 2003-4 figures. But it is still not clear how many who train in Wales take up posts here and how many drop out after a few years.
In the report, Estyn calls on the Assembly government to fund EPD courses for teachers in their second and third years in small schools more flexibly so they are not disadvantaged.
Estyn was asked to investigate provision of the funded three-year development programme to see if it was helping teachers to stay in teaching long-term.