Mathematical learning to implant the concept of algebra operation using constructivism approach is very important. Students should be actively involved in the process of building their understanding, so meaningful learning experiences can be to gained. This research was an experimental research involving 91 students of grade 8. This research applied constructivism-based mathematics module used by the students during studying the concept of algebra operation. The result showed that the use of constructivism based mathematics module was very effective in improving students' mathematical understanding on algebra operation material. This result was obtained by performing the initial test (pre-test) before the use of modules and final test (post-test) after the use of module.  Addition, the result of observation conducted during the learning activities showed that in the use of modules in learning mathematics, students with high academic ability tended to be more active in the discussion process.

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