This study assessed the effects of a collaborative mentoring sequence on the professional development of a preservice teacher (PT). The analysis of data from observation and self-confrontation interviews identified work rules [Wittgenstein, L. (1996). In G. E. M. Anscomb & G. H. Von Wright (Eds.), "Remarques philosophiques" ["Philosophical investigations"]. Oxford: Blackwell] that were learned and/or used by the PT and from which we were able to evaluate his professional development. By following the trace of these rules, we showed that in some circumstances collaborative mentoring provides a better articulation between traditional training situations (co-preparation and co-evaluation of lessons) and the classroom situation than traditional models. From a description and discussion of these circumstances, the conditions for applying these findings to optimize training programs are discussed.