Topical transitions in teachers' classroom talk were analyzed from the perspective of conversations as game-like structures with "moves" as basic elements. Three devices observed in this conversational context were proposed as having topical boundary functions: "framing" moves (words like O.K., alright), "pointing" moves (speech which notes the speaker's fact of saying something), and "quantifying" moves (speech with a logical or numerical quantifier which organizes subsequent talk). Preliminary evidence was presented which supported the hypothesis that these moves in fact bound topic talk. (13pp.)