In the present research, effective and ineffective activities that secondary school teachers used and their perceptions on the effectiveness of the activities are investigated. The data were collected from 20 teachers using semi-structured interviews. Data were analysed using open coding and directed content analysis. Research findings showed that the type, cognitive process and ambiguity characteristics of instructional tasks do not differ between effective and ineffective activities. However, findings revealed that effective activities concentrated on cooperative rewards and small group study, whereas ineffective activities occurred in an individualized study and individualistic reward characteristics. Teachers' criteria of activity effectiveness was factors related to implementation process, such as the engagement and students' enjoyment. Teachers associated the effectiveness and ineffectiveness of the activities with the contextual features, such as students' characteristics, course material and classroom environment.