This study was conducted to examine the effects of functional communication training when used by mothers to address the serious challenging behaviors of toddlers. Multiple baseline (across home routines) designs were used with two mother-child dyads. The data showed mothers used the procedures correctly and interventions produced reductions in the children's challenging behaviors and increases in their use of communicative replacement skills. Social validity data supported the clarity of the effects and indicated that the procedures were viewed by the mothers as feasible and as having acceptable contextual fit. Results are discussed in relation to the importance of resolving challenging behaviors early in a child's life, and the need for additional research on effective strategies that can be used by typical intervention agents in natural settings. (Contains 2 tables and 4 figures.)