Three-, 4-, and 5-year-olds performed Tower of London problems under spoken, manual, and combined (requiring both spoken and manual) response conditions. Preschoolers' solutions were most goal-focused when required to give only a spoken response, intermediately goal-focused when required to give both response types, and least goal-focused when required to give only a manual response. Preschoolers' depth of search was longer in the spoken response condition. Three-year-olds performed poorly in all conditions. Surprisingly, only the condition requiring a spoken response resulted in significant age differences between 4- and 5-year-olds in solution efficiency. In general, the results support theories of increased inhibitory ability and increased conscious cognitive control as mechanisms critical to executive-functioning development. (Contains 3 figures, 1 table, and 1 footnote.)