This study originates from an ELT curriculum innovation in Benin,leading to the adoption of a textbook which emphasizes the development of communicative skills, chiefly through pair/group work. It describesthe experimental INSET set up to introduce its new methodology, and which has been evaluated through the comparison of teaching and learning by experimental classes with control classes. It also identifies, through a questionnaire, INSET processes considered as most effective. It finds that teachers with the Action-Research based INSET improved their abilities to use the new book for more communicative teaching as seen through the evaluation of teacher performance by inspectors, pupils and teachers themselves and as compared with control group teachers. It also finds that the project and the implementation of the curriculum it aimed to facilitate did not adversely affect pupil progress. On the contrary the experimental group pupils scored moderately higher than the control group pupils -on all the English general proficiency tests used for the study. But the difference is not statistically significant. However, the experimental group pupils' subjective impression of progress as well as their views on communicative language teaching are significantly more positive than those of control pupils. It also finds that diagnostic class observations, practical workshops at school based INSET meetings and residential seminars, with active involvement of teachers through action research, and formative class observations, are considered as more effective than summative class observations, feedback and advice by trainers and inspectors. It concludes that priority should be given to in-service education to ensure the success of the curriculum reform, with a systematic programme drawing on the problem solving approach to educational innovation for ELT. This should be progressively- generalised to other subjects. Some suggestions are also made as to the contextualisation and relevance of communicative teaching.