<![CDATA[The urgency of this study lies in addressing students’ difficulties in connecting multiple chemical representations and developing higher-order thinking skills when learning acid–base concepts. This research is motivated by the low level of higher-order thinking skills of Indonesian students due to learning that does not involve students actively. This study describes the effectiveness of the Predict, Observe, Explain (POE) learning model on acid-base material based on multiple chemical representations to improve higher-order thinking skills. This study is a quasi-experimental study with a non-equivalent pretest-posttest control group research design. The population in this study were all students of grade XI MAN 1 Bandar Lampung in the 2025/2026 academic year from grades XI F1.1 to XI F1.7. The sampling of this study used a purposive sampling technique. The instruments used were a high-order thinking skills test, an observation sheet for the implementation of the learning model, and an observation sheet for student activities. The research data were analyzed by testing the difference between two means using the Independent Sample t-Test. The results of the Independent Sample t-Test showed that the average n-Gain of students' higher-order thinking skills in the experimental class was 0.73, while the average n-Gain of students' higher-order thinking skills in the control class was 0.57. Based on this, it can be concluded that the POE learning model on acid-base material based on multiple chemical representations is effective in improving higher-order thinking skills.]]>
