This study compared the effects of 2 supplemental interventions on the beginning reading performance of kindergarteners identified as at risk of reading difficulty. Students (N = 206) were assigned randomly at the classroom level either to an explicit/systematic commercial program or to a school-designed practice intervention taught 30 min per day in small groups for approximately 100 sessions. Multilevel hierarchical linear analyses revealed statistically significant effects favoring the explicit/systematic intervention on alphabetic, phonemic, and untimed decoding skills with substantive effect sizes on all measures except word identification and passage comprehension. Group performance did not differ statistically on more advanced reading and spelling skills. Findings support the efficacy of both supplemental interventions and suggest the benefit of the more explicit/systematic intervention for children who are most at risk of reading difficulty. (Contains 6 tables and 1 figure.)