Purpose: Although conversational recast treatment is generally efficacious, there are many ways in which the individual components of the treatment can be delivered. Some of these are known to enhance treatment, others appear to interfere with learning, and still others appear to have no impact at all. This study tests the potential effect of clinicians' recast length on child learning during a recast treatment. Method: Twenty-six preschool children were treated for grammatical errors using Enhanced Conversational Recast Treatment. Half heard recasts of four or fewer words (Short Recast condition), and half heard recasts of five or more words (Extended Recast condition). Outcome measures included generalization of the treated grammatical form, spontaneous use of these forms, change in mean length of utterances in words, and the number of children in each condition who showed a clinically meaningful response. Results: There was strong evidence of improvements in the use of grammatical forms targeted by the treatment compared with forms that were tracked but not treated. Twenty children (11 in the Short Recast condition and nine in the Extended Recast condition) showed a clinically meaningful response. There was minimal support for the hypothesis that the length of clinician utterance influenced either progress on a grammatical form targeted by the treatment or on the child's mean length of utterance in words. Conclusions: The study adds to the evidence for the efficacy of Enhanced Conversational Recast Treatment. However, there is little evidence that clinicians need to regulate the length of the recast they provide to children.