This research evaluates the impact of a training programme on trainee physics and chemistry teachers, focusing on the way pupils' explanations are dealt with during teacher-pupil interaction. The population is composed of 10 teachers and 303 pupils, from which the experimental sample was taken (8 teachers and 172 pupils). The qualitative analysis of the recordings of the sessions shows that teachers, after training, are more ready to take pupils' productions into account, use a greater number of appropriate arguments, and are more frequently aware of pupils' misconceptions. A quantitative analysis of the achievement of pupils whose teachers followed the complete programme indicates that pupil outcomes improve. The conditions required for this training to be effective are also explored.