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Abstract. The aim of this study is to get an in-depth understanding of students' abstract-thinking ability in mathematics learning. This study was an experimental research with pre-test and posttest control group design. The subject of this study was eighth-grade students from two junior high schools in Bandung. In each schools, two parallel groups were selected and assigned into control and experimental groups. The experimental group was exposed to Cognitive Apprenticeship Instruction (CAI) treatment, whereas the control group was exposed to conventional learning. The results showed that abstract-thinking ability of students in experimental group was better than that of those in control group in which it could be observed from the overall and school level. It could be concluded that CAI could be a good alternative learning model to enhance students' abstract-thinking ability. IntroductionAbstract-thinking ability in mathematics learning is very important for students to develop. Mathematics abstraction is a process of the building a continuous mathematical knowledge from concrete to abstract. Abstraction is a fundamental process both in mathematics and in mathematics education [1]. The abstraction is a natural process with full awareness as mind focuses on several aspects of circumstances to make a decision and process of making such concrete situations by finding new meaning in order to establish interconnections within the different elements of the whole [2] [3]. In fact, junior high school students' abstract-thinking ability in Bandung is still relatively low [4] [5].The indicators of abstract-thinking ability in this study are: (1) the ability to transform problems into symbolic form; (2) the ability to construct an equation; (3) the ability to state relationship between the concept of geometry shapes and linear equations; (4) the ability to make generalizations; and (5) the ability to make equations according to the given situation [4].According to Yusepa, teachers have an important role in learning process and improving national education and become guidance. Furthermore, Yusepa states that in order for learning to be meaningful, the teacher should be able to teach students with varied models or learning approaches [6] [7].The effective of teacher characteristics are caring, assertive, modeling and enthusiastic, and has high expectations. Teacher's awareness in organizing the classroom or succeeding in all teaching sections