Science teaching in the 21st century society is a challenge but with the aid of effective and appropriate instructional materials, student learning is enhanced. This descriptive research sought to test and validate the teacher-made Science workbook in Grade 8. The quasi-experimental method of research was utilized in the study. Quasi-experimental test causal relationships, much like true experimental designs. A conceptual test in Science was used to assess the level of proficiency of students and served as the basis for the development of the instructional material. Meanwhile, a researcher-made evaluation tool was used to assess the developed material’s usefulness. Results revealed that the students’ performance in Science before the use of the teacher-made workbook is Fairly Satisfactory based on the pretest mean. Meanwhile, their performance in Science after the use of the teacher-made workbook is Very Satisfactory based on the post-test mean. According to the findings, there is a substantial difference in students' Science performance before and after using the teacher-made Science workbook. Similarly, the second quarter academic grades and pretest scores have a low positive significant link, while the third quarter academic grades and post-test scores have a negligible negative significant relationship. The study recommends that performance tasks, written works, and quarterly exam, may be considered as variables of academic performance in further investigation. The developed workbook can be used by Grade 8 Science teachers to enhance students’ performance in the subject and can be a good tool in developing students’ scientific literacy. The teacher-made Grade 8 Science workbook can also be used by teachers as a supplementary material in the K to 12 Curriculum.