This paper examines a specific aspect of systematic variability, which is taken to be a result of influence of linguistic context on interlanguage (IL) performance. While it is important to describe how or under what circumstances a linguistic context exerts an influence on IL development, one also needs to explain why it occurs. On the basis of a second-language study that examines the development of wh-movement in different extraction sites among a group of Chinese learners of English, an analysis of this type of systematic variability is proposed in terms of typlogical characteristics inherent in these extraction sites. Wh-movement in English is chosen because cross-linguistic comparison reveals interesting differences between Chinese and English. The results suggest that there is internal consistency in the way learners apply wh-movement to a range of permissible contexts. It is reflected by stages of development in which the learner's initial knowledge is observed to undergo a process of reorganization as new information about the potential contexts that permit wh-movement is gradually incorporated into his IL grammar. During this process of linguistic reorganization, the subjects' performance is observed to vary depending on which stage of IL development he is at, and the internal properties of the linguistic context in which the movement rule may occur. (Author/JL)