This paper is related to an investigation carried out by researchers from a Brazilian public institution (Federal University of São Carlos) and experienced elementary school teachers. It adopts a research and intervention methodology developed in an online continuing teacher education programme, whose aims were the development of mentoring activities to help novice teachers to lighten their everyday professional difficulties. The intertwined research questions could be formulated as: (a) what contributions the participation of mentors in a research group could offer in their professional development processes? (b) How these mentors appropriate the current knowledge in the area in order to have theoretical and methodological tools for their management of beginning teachers? and (c) How they make explicit their professional practical knowledge? The online mentoring programme has promoted the establishment of professional and affective bonds among the participants, the broadening of professional knowledge, the collaboration among peers, the mastery of online adult education technologies and the participants' professional growth. It should be noted that it has been a much more complex enterprise than a face-to-face equivalent programme would have been because it demands entirely new logistics and some challenges. This text focuses on the learning of mentors as well as the potential of the investigative tools used considering the professional development of mentors, as well as a way to comprehend such process.