The purpose of this article is twofold: to describe a prototype for a computer-assisted task-based language instruction (CATBI) tool designed and developed for Turkish as a Foreign Language, and to report on the effectiveness of the CATBI tool. More specifically, this work discusses an experimental study that examined the role of teaching approach in foreign language development by comparing CATBI to computer-assisted form-focused language instruction (CAFFI) on language production in terms of accuracy, lexical complexity, and fluency. For a duration of 7 days, two intermediate-level Turkish as a Foreign Language classes consisting of 28 high school students participated in this experiment. The classes were randomly assigned to two treatment groups: an experimental group with CATBI and a control group with CAFFI. Statistical analyses revealed that students in the CATBI group produced significantly better and more fluent language than students with CAFFI. However, no significant effects were found in terms of accuracy and lexical complexity of the language produced. Based on these results, it was concluded that CATBI is more effective than CAFFI in enhancing language production in general, and fluency in particular. (Contains 2 tables and 12 figures.)