An intervention experiment served to evaluate the efficacy of highly guided discovery learning of relations underlying add-1 and doubles combination families and to compare the impact of such instruction with minimally guided instruction. After a pretest, 78 first graders were randomly assigned to one of three intervention conditions: highly guided add-1, highly guided doubles, or minimally guided add-1 and doubles practice-only. Each highly guided intervention served as an active control for the other. The practice-only intervention served to control for the effects of extra practice. For both the add-1 and the doubles strategies, the highly guided intervention, but not the practice-only control, was more successful (as indicated by effect size) than the active control in promoting meaningful transfer to unpracticed but related combinations. The highly guided doubles intervention, but not the highly guided add- 1 intervention, produced greater transfer than the minimally guided practice-only intervention.