Peers discussion of contradictory ideas has been proven to promote students learning. Some empirical evidence suggests that whole-class argumentation has similar benefits, but there is no clarity yet on whether discussion accounts for this effect. This study aimed at testing the effects of different aspects of whole-class argumentation on science learning. A non-probabilistic sample of 220 students (aged 10 to 11 years) from 18 public schools in Santiago, Chile, participated in the study. Eleven teachers delivered lessons according to a teaching programme especially developed to foster argumentation (intervention group) and 7 teachers delivered lessons in their usual way (control group). Students were assessed individually using pre- and post-measures of learning, argumentative skills and attitudes toward science. The two formers were tests and the latter was a questionnaire. Lessons were videotaped. Factorial analysis and linear regression were conducted. Results showed that 2 factors predict a portion of the variance on learning: one factor composed of justificatory utterances and the other of students counter-arguments. These results suggest that contradiction among peers is not the only aspect of classroom argumentation that prompts learning.