The research objectives were to 1) study the current conditions, problems, and good practices regarding teaching and learning 2) develop a blended instructional model using problem-based learning with graphic organizers to enhance systems thinking skills in computational science for students in lower secondary school and 3) study the results of using the instructional model. The research and development process was divided into 3 phases. Phase 1; study the current conditions, problems, and good practices regarding teaching and learning, the sample group included 368 teachers and 11 teachers. Phase 2; develop a blended instructional model, the sample consisted of 8 and 7 experts, and Phase 3; study the results of using the instructional model, the sample consisted of 35 grade 7 students. Data were analyzed using basic statistics and hypothesis testing statistics. The research results found that 1) Current conditions and overall problems were moderate level. The good practices included blended learning methods, problem-based learning, and instructional media with graphic organizers 2) The blended instructional model using problem-based learning along with graphic organizers included 4 core components: principles, objectives, management of teaching-learning processes, and measurement and evaluation. Five experts evaluated and certified this instructional model as appropriate in all aspects at a high level. 3) The results of using the instructional model found that (1) the systematic thinking skills of students who studied using the instructional model overall post-test were significantly higher than pre-test at the 0.05 level. (2) Measuring students' learning achievement overall score post-test was significantly higher than pre-test at the 0.05 level. (3) students' post-test scores of the experimental were significantly higher than the control group at the 0.05 (4) students' post-test scores of the experimental were significantly higher than the control group at the 0.05.