The study considers the impact of a program for social and emotional learning in Swedish schools on use of drugs, volatile substances, alcohol and tobacco. The program was evaluated in an effectiveness study. Intervention students were compared longitudinally with non-intervention students using nonparametric latent class analysis to identify subgroups of students with similar use levels and trajectories. Statistically significant intervention-by-duration interactions, with medium to large effect sizes to the advantage of the SET students were found for all substances in one or more, but not all, of the latent classes. Favorable trajectories were found for non-users/light users of drugs, moderate sniffers, non-users/light users of alcohol, and occasional smokers. Only among heavy smokers was there a possible iatrogenic effect of SET. Such programs, given a duration of two years or more, may dampen increases in use with age and discourage early debut, although they are not specifically targeted at use itself. (Contains 2 tables and 4 figures.)