There are many recognised forms of teacher professional development ranging from simply reflecting on a lesson recently taught to enrolling in a formal course at university. This study set out to examine the perceived effectiveness of one mode of professional development, a spaced learning activity(SLA). The SLA was selected for a number of reasons. Firstly, current government economic and industrial policy includes an emphasis on the training and retraining of the Australian workforce as an economic necessity. Within this policy, teacher professional development is considered to improve the quality of teaching and to raise professionalism. Secondly, the literature in the area suggests that professional development activities have the potential to improve the quality of teaching by enhancing teachers' knowledge and skills. Thirdly, an SLA appeared to incorporate many characteristics of effective professional development which are identified in the literature, for example, allowing time for critical reflection and for internalising concepts. This study sought to determine the effectiveness of an SLA as a training strategy and in enhancing teachers' knowledge, beliefs, classroom practice and students' learning outcomes and also to identify characteristics of an SLA which assisted and inhibited its effectiveness. Perceived costs and benefits of participation to the individual teacher were also evaluated.. The study was carried out at Marist College, Canberra , a Y7-12 single sex secondary school with an enrolment of approximately 1100 boys. The study involved twenty five teachers who participated voluntarily in a pilot collegial group programme at the school during 1993. The term "collegial group" is used for a small group of professionals who meet on a regular basis to learn together and to support one another in their on-going professional development. Adie (1988:4) explains that collegial groups are designed to assist in supporting, learning, problem solving, planning and performing. The twenty five volunteers were divided into three groups. Each group determined its own 'focus1 and met on an average of five occasions over six months, for meetings ranging from two to four hours. The foci selected by each group were: Increasing student motivation Increasing student responsibility for learning. Excellence in Teaching course. Meetings usually provided an opportunity for individual feedback on teaching changes tried, some input on the focus area, discussion of its practicality and a commitment to try something new and to report back at the next meeting. Some groups also included discussion of specific teaching and learning 'problems', where the group would offer solutions. A variety of data collection techniques were employed in the study. A questionnaire was conducted before the programme commenced to ascertain participants' expectations and concerns about the programme and anticipated effects of participation on their teaching knowledge, beliefs and practice and on their students' learning outcomes. A questionnaire was also administered at the end of the programme. The post-study questionnaire sought participants' perceptions about how well their expectations for the programme had been met, any differences participation had made to their teaching knowledge, beliefs and practice, and to their students' learning outcomes and whether these differences constituted improvements. Further questions covered: the benefits and costs to individuals of participation in the programme; the benefits participants perceived that other non-participatory colleagues could derive from a future programme; and the perceived value of the activity as a mode of professional development. The questionnaire also included a table covering organisational factors of the programme and elicited participants' responses about the degree to which each assisted and inhibited progress. In addition to the questionnaires, structured interviews were conducted with the participants after the completion of the programme asking similar questions about their perceptions of its success. Analysis of a variety of data collected through pre and post-programme questionnaires as well as interviews clearly indicates that this mode of delivery was perceived by the participants to be an effective form of professional development from the perspective of changing teaching knowledge, beliefs and practice, and as a refocussing or confirming activity by providing stimulus to an individual's professional development. Further data collected support the organisational characteristics of this SLA and provide some suggestions for changes. Finally, the findings clearly show that the benefits to individuals of participation are perceived to outweigh the costs, further supporting the effectiveness of this mode of professional development.