As Mathematics is a subject of practice, printed instructional materials like workbooks will help learners exercise their skills in Math and at the same time monitor their learning progress. This action research was conducted to determine the experiences and effect of using a developed workbook in teaching word problems involving Linear Equations in One Unknown among a group of Grade 7 students in JBT Caing Sr. Memorial Integrated School, Tambilil, Kiamba, Sarangani Province. This investigation employed quantitative research design, through quasi-experimental and interview. Forty (40) students were divided into the control and experimental group, in which the control group was taught using the traditional method and the experimental group experienced learning with the use of a developed workbook. T-test results revealed that there is a significant difference between the mean gain scores of the experimental and the control group, showing that the use of the workbook is more effective and elicited higher scores than those under the traditional way of learning. Through a focus group discussion, the students who used the developed workbook found the material convenient to use, and helpful in solving word problems. With this, the developed workbook can be used as a supplementary teaching-learning material in a Mathematics learning space.