This study aimed at determining the effect of reform-based-instructional method learning styles on students' achievement and retention in mathematics. A sample size of 119 students was randomly selected. The quasiexperimental design comprising pre-test, post-test, and randomized control group were employed. The Collin Rose learning styles identification and Mathematics instrument were used for data collection. Data collected were analyzed using mean, standard deviation and analysis of covariance. Results revealed that students taught Mathematics with reform-based instructional method performed better than students taught the same mathematics content with the traditional method. Also, students' achievement in mathematics was influenced by the students' leaning styles. For effective teaching and learning in Mathematics, there should be reforms in the instructional processes, taking into consideration the influence of the students' learning styles in particular.