Objective We evaluate the effectiveness of a swim skill acquisition intervention among Latino youths, ages 3–14, a minority population at increased risk of drowning.

Methods Parents were recruited through community institutions to have their children participate in group swim lessons. Each child's swim ability was assessed at baseline, and they were then exposed to swim lessons over an 8-week period, taught by trained professionals. The swim skill curriculum focused on water safety, flotation and endurance, at five levels of increasing skill acquisition. Final swim ability was assessed on the last day of the child's participation. Programme effectiveness was measured using direct pre–post comparisons with and without adjustment for key moderators (age and gender) and a mediator (number of practices). We also present a bias-adjusted estimate comparing low with high practice volume relying on a propensity score analysis.

Results Among the 149 participating children, average acquisition was 12.3 swim skills (95% CI 10.7 to 14.1). Skill acquisition varied by age category (3–5, 6–9 and 10–14 years) and by gender. We found a strong practice intensity effect, with skill acquisition accelerated for those participating in 10 or more swimming lessons. The propensity-adjusted estimate of the impact of 10 or more compared with 9 or fewer lessons was 8.2 skills (95% CI 4.8 to 11.8).

Conclusions An 8-week swim intervention is effective at building skills in a community-based sample of Latino children, ages 3–14 years. The number of swimming lessons was a far stronger correlate of skill acquisition than were age or gender.