In ‘Thinking Aloud Pair Problem Solving’ (TAPPS), students work in pairs to solve the mathematics problems. One student (the problem solver) is required to read the problem and think aloud during the problem solving process. Another student (the listener) attends to the problem solver’s thinking and reminds him/her to keep saying aloud what he/she is thinking or doing, while also asking for clarifications and pointing out errors being made. This study explored the effectiveness of applying TAPPS on students’ mathematics performance in Brunei Darussalam. A Year 9 class from one of the secondary schools participated in this research study. The students’ problem solving behaviour and mathematics achievement were investigated to see any significant differences after learning using the TAPPS method. Data reported were mainly collected through mathematics achievement tests, questionnaire surveys and classroom observations. The study revealed that there was a significant improvement in students’ problem solving behaviour especially in understanding the problem. Although TAPPS did not help in improving students’ conceptual knowledge in mathematics rather, it required the students to have a strong grasp of the conceptual knowledge beforehand in order to be able to devise a plan to solve the problems.