This study investigated the effects of problem solving-based instruction versus lecture-based direct instruction on student academic achievement and attitude. Evidence of student achievement and attitude was collected through a quasi-experimental quantitative methodology. Two classes were used, one as an experimental group being taught with Problem-Based Learning (PBL) and one as a control group being taught with Direct-Instruction (DI). The length of instruction was a two-week unit on basic triangle properties in Geometry. A pre-test and post-test was given to the participants followed with a student attitude questionnaire survey. The data analysis included a t-test with the pre-test and post-test data to determine the significance of learning achievement and a chi-square analysis with the survey data to determine the significance of student attitude towards a particular instructional method. The researcher concluded that a significant gain in student achievement and attitude did occur with the PBL class.