Abstract

The purposes of this study were to develop the mathematical problem-solving ability of Thai Grade 8 students using the Open Approach in learning surface area and volume and to examine whether students could achieve the established criterion of 70% of the full score. The research was designed as an action research study following a cyclical process of planning, action, observation, and reflection. The participants were six Grade 8 students from Ban Khonkaen (Nikornrat Sattakarn) School, Roi Et Province, who were selected by purposive sampling based on their low mathematical problem-solving ability. The research instruments included Open Approach learning management plans, mathematical problem-solving tests, semi-structured interviews, and observation and reflection records. Quantitative data were analyzed using mean, percentage, and standard deviation, while qualitative data were analyzed using content analysis. The findings indicate that the implementation of the Open Approach was associated with gradual improvement in students’ mathematical problem-solving performance and problem-solving processes across the action research cycles. Students demonstrated improvement in planning solution strategies, explaining reasoning, and verifying answers, although some students continued to experience difficulties in complex geometric problem-solving tasks. This study contributes evidence that the Open Approach, when implemented through reflective action research and continuous instructional adjustment, can support the development of mathematical problem-solving ability among low-achieving students in geometry learning.

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