The objectives of this research were to study issues around the management of science learning, problems that are encountered, and to develop a learning management model to address those problems. The development of that model and the findings of its study were based on Constructivist Theory and literature on reasoning strategies for enhancing critical thinking among secondary school students. In the demonstration project of the developed model, two classes of grade 9 students were selected. One class of 33 students and another of 30 students became the experimental and control groups, for instruction based on the learning management model (experimental), and the traditional approach (control). This research used a Research and Development methodology (R&D), which included three phases for implementation. The research findings found that the teachers who implemented the learning management model assessed its usefulness at a "moderate" level. In addition, they agreed about the need for such a model for enhancing critical thinking at "the highest" level. Evaluation of one of the models found it to be appropriate at "the highest" level and the effectiveness of the model conducted from post-tests of critical thinking ability scores was 76.30/77.47. The effectiveness score conducted from the perspective of academic achievement was 76.30/76.67. The students who participated in the experimental group obtained a higher score on the post-test on critical thinking ability at 0.05 level of significance. In addition, the experimental-group students obtained a higher level of post-test scores in both critical thinking and academic achievement than the control group at 0.05 level of significance.