This article uses activity theory to consider how teacher learning and development occurs. It aims to show that imitation and orienting activity, both of which make use of the analysis of actions into means and goals, can help explain how a group of Malaysian mathematics and science teachers learned to use the language-teaching practice of tasks for English medium content teaching. It focuses on four Malaysian mathematics and science teachers who participated in a teacher-development programme by comparing their peer microteaching lessons on weeks 2/3 and 10 of the programme. The findings show that the teachers learned to use tasks by being able to successfully imitate some task criteria before others, with the crucial criterion of a "gap" being particularly difficult to imitate. This suggests they were orienting to tasks through incomplete images, possibly because of their prior experiences as content teachers. Role reversal helped clarify their images of tasks, enabling faithful transmission to occur. This study concludes by suggesting that imitation and transmission are important to teacher development, and that further research using Galperin's orienting activity is called for. (Contains 1 table.)