Purpose: We examined the effects of practice on color naming of neutral and interfering stimuli. Word reading is correlated with color naming and with Stroop interference, in which color words are printed in a different color ink which must be named. It is often assumed that interference arises from lack of automaticity of color naming and might decrease with naming practice. Method: 58 adults and 66 children (Grades 4-5) formed 4 groups and practiced for 3 days on 192 stimuli (144 for children) each day. The “interference” group practiced color naming with incongruent color words; the “color” group practiced color naming with strings of Xs; the “word” group practiced reading aloud color words; the “control” group did not practice. The days before and after practice each participant read color words and named colors of neutral stimuli and incongruent color words. Reading and inhibition tests were also included. Results: Interference practice led to decreased interference for both adults and children. Color practice did not reduce color naming time and did not affect interference. Word practice reduced children’s (but not adults’) interference. Interference changes could not be attributed to reduced impulsivity or improved cognitive control. Conclusions: Findings are inconsistent with lack of color naming practice being a major cause of interference. Rather, word reading seems to be the limiting factor, because practice at an age when reading is not yet fully fluent leads to reduced interference. Studies of interference help us understand the development of word reading efficiency and associated cognitive control.