This study examined a literacy program that targeted students most at risk of reading difficulties in kindergarten and first grade of 12 Swedish schools. The program used multi-sensory learning methods that focused on phonological awareness and phonics, and was delivered during 10 weeks over 30-35 sessions by teachers in a one-to-one or one-to-two setting. In total, 161 students aged 6-7 years were randomly assigned to a treatment group or a waiting list control group. The treatment group showed large and statistically significant improvements compared to the control group on the two pre-registered primary outcome measures: a standardized test of decoding (Hedges' g = 1.07) and a standardized test of letter knowledge (g = 1.03). The improvements were also significantly larger on measures of phonological awareness (g = 0.56) and self-efficacy (g = 0.57), but not on measures of enjoyment and motivation. The program appears cost-effective relative to other tutoring programs.