Purpose: This study examined language productivity and syntactic complexity in school-age children in relation to their knowledge of the topic of discussion--the game of chess. Method: Children (N = 32; mean age = 10;11 [years;months]) who played chess volunteered to be interviewed by an adult examiner who had little or no experience playing chess. Children's chess knowledge and experience was assessed, and each child was classified as a novice or an expert player. Each child participated in 3 speaking tasks: General Conversation, Chess Conversation, and Chess Explanation. Interviews were audio recorded, transcribed into Systematic Analysis of Language Transcripts (J. F. Miller & R. Chapman, 2003), segmented into T-units, and coded for finite clauses. Each speaking task was analyzed for total T-units; mean length of T-unit; clausal density; and nominal, relative, and adverbial clause use. Results: Total T-units, mean length of T-unit, clausal density, and the use of each type of subordinate clause was substantially higher in the Chess Explanation task compared with the Chess Conversation task or the General Conversation task. Compared with the novices, the experts knew more about chess, had played longer, and were stronger players. Nevertheless, the novices and experts did not differ on any of the language factors for any of the speaking tasks. Conclusions: Language productivity and syntactic complexity in school-age children are strongly influenced by the speaking task. When children are presented with a motivating and challenging topic, they rise to the occasion to explain the finer details of it to a naive adult. (Contains 6 tables, 4 figures and 1 footnote.)