A follow-up to the Sävajö school project, a universal intervention, from 1998 to 2002 is presented in this paper. The project was a cluster-randomised trial aimed at improving the literacy of beginners from the perspective of factors like achivements, mental health, school satisfaction, and reading capacity at the end of grade 3, while using an alternative curriculum. Half of all the six-year-olds (n = 92, of whom 48 attended single-age classes and 44 attended mixed-age ones) starting kindergarten were assigned to the intervention group. The comparison group (n = 85) followed the regular curriculum. The follow-ups after grades 9 and 12 show that the improvements observed after grade 3 persisted at the end of grade 9 in the experimental group attending single-age classes, but were not sustained for those who had atteded mixed-age classes. The students who had attended the experimental single-age classes were more likely to have completed their studies at the end of grade 12.