This study is about the design, validation, and effectiveness of instructional materials regarding the proper use of words and phrases in Filipino. The study utilized an experimental design and Cluster Sampling in selecting participants. The research aims to determine the design, validation, and effectiveness of instructional materials on correct language use in Filipino based on scores provided by eight teachers specializing in Filipino from Laguna State Polytechnic University, Santa Maria Integrated National High School, Famy Integrated National High School, and Siniloan Integrated National High School, along with the scores obtained from one hundred students (fifty students in the control group and fifty students in the experimental group) from Grade 7 in pre-test and post-test assessments. Findings from this study revealed that the instructional materials developed by the researcher were effective, thus recommending the development of additional materials such as modules for the Filipino subject, which could aid in enhancing student learning. Secondly, the use of modules was found to be effective in student learning, prompting schools to conduct training in module creation for comprehensive understanding and learning. Thirdly, researchers associated with this study discovered the benefits of using modules.