ABSTRACT
The purpose of the study was to investigate and determine the effect of using mathematical manipulatives in teaching Theorems on Triangle Inequalities for Grade 8 STE students at San Jose National High School in Antipolo City. Purposive sampling was used by the researcher to create a One Group Pretest-Posttest Quasi-Experimental Design; students from three Grade 8 STE sections (Mendel, Descartes, and Milton) participated in the study under the blended learning modality. Each of seventy (70) participants was exposed to mathematical manipulatives. Experts validated the researcher-made assessment before administering it to the participants. Data were gathered from the participants using the Pretest-Posttest assessment made by the researcher, which is aligned to the competencies of the K-12 curriculum. The results of the pretest and posttest were compared through T-test. The result showed that using the 0.05 level of significance, the Pretest and Posttest significantly differed. The study was limited to three Grade 8 sections consisting of seventy (70) students under the Science, Technology, and Engineering Program (STE). Using mathematical manipulatives in teaching Geometry increased the posttest scores of Grade 8 students. It was found out that it developed the critical thinking skills and creativity of the students. The use of mathematical manipulatives is recommended for teaching Theorems on Triangle Inequalities and can also be used for other topics in mathematics at different levels.