It has been suggested that a child's productive phonological knowledge may be one factor that potentially accounts for individual differences in generalization learning observed among phonologically disordered children (Dinnsen & Elbert, 1984; Elbert, Dinnsen, & Powell, 1984). This paper evaluates the hypothesis that productive phonological knowledge influences generalization. Three related studies involving 6 functionally misarticulating children were conducted. In the first study, a description of each child's phonological system was developed using procedures of standard generative analysis. Based upon these descriptions, each child's productive phonological knowledge of his or her own sound system was determined and then ranked on a continuum ranging from "most" to "least" knowledge relative to the adult target. The second study implemented an experimental treatment program based upon each child's productive phonological knowledge, with treatment sounds selected directly from each child's continuum of knowledge. The third study reassessed each child's productive phonological knowledge following treatment. The results of these three studies indicated that a child's productive phonological knowledge of the sound system influenced the overall amount of generalization learning. However, the extent of generalization learning was associated with the point on the knowledge continuum at which treatment was initiated. These findings are discussed with reference to individual differences in generalization learning.