This study examines the relationship between different types of conversational interaction and SLA. Long's (1996) updated version of the interactionist hypothesis claims that implicit negative feedback, which can be obtained through negotiated interaction, facilitates SLA. Similar claims for the benefits of negotiation have been made by Pica (1994) and Gass (1997). Some support for the interaction hypothesis has been provided by studies that have explored the effects of interaction on production (Gass & Varonis, 1994), on lexical acquisition (Ellis, Tanaka, & Yamazaki, 1994), on the short-term outcomes of pushed output (see Swain, 1995), and for specific interactional features such as recasts (Long, Inagaki, & Ortega, 1998; Mackey & Philp, 1998). However, other studies have not found effects for interaction on grammatical development (Loschky, 1994). The central question addressed by the current study was: Can conversational interaction facilitate second language development? The study employed a pretest-posttest design. Adult ESL learners (N = 34) of varying L1 backgrounds were divided into four experimental groups and one control group. They took part in task-based interaction. Research questions focused on the developmental outcomes of taking part in various types of interaction. Active participation in interaction and the developmental level of the learner were considered. Results of this study support claims concerning a link between interaction and grammatical development and highlight the importance of active participation in the interaction.