Analyses of classroom interaction have frequently spotlighted reasoned dialogue as beneficial for student learning, and research into small-group activity amongst students offers empirical support. However, the evidence relating to teacher-student interaction has never been compelling, and one of the few studies to investigate the issue directly detected no relation whatsoever between reasoned dialogue and learning outcomes. The present paper outlines additional data from that study, together with evidence from elsewhere, with a view to interpreting the results relating to reasoned dialogue. Account is taken of the generally positive evidence obtained from studies of group work amongst students. The key proposal is that it may be reasoned opposition that promotes learning rather than reasoned dialogue in general, and reasoned opposition is probably rare when teachers are involved. The proposal has implications for both the dialogic and the argumentation perspective upon classroom interaction, and these are discussed.