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Instructional method is an important aspect of teaching and learning to determine the activities of teachers and students. Appropriate instructional methods influence many motivational variables of learners such as tendency to think critically. This research aims to determine the effects of usage of instructional methods for training students’ thinking skill on environmental learning. This study is quasi-experimental design of post test only. Two equivalent student groups in secondary school were offered a topic on environmental learning with different instuctional methods. The instructional methods were laboratory method and discussion method. The teacher was given to the first group using laboratory method, while the second group was given using discussion method. Effectiveness of different instructional methods was measured quantitatively by an achievement test. The analysis result of post test showed that there was significantly different between first group and second group at a significance level of 0.05 for the interest of the first group. According to these findings, we suggest applying laboratory method instead of discussion method for training students’ thinking skill on environmental learning.