This study explored the effect of blended learning in terms of model-based collaborative learning in a small private online course (SPOC) environment on 10th graders' achievements in stoichiometry through a quasi-experimental design. The participants included 140 tenth graders assigned to two groups: (a) the experimental group, which studied in a blended environment (N = 69) and (b) the control group, which studied in a conventional lecture-based environment (N = 71). The results revealed that the experimental group exhibited significantly superior performance than the control group after the intervention and that the key factor in enhancing students learning is the teacher's facilitation. These findings implied that the blended model-based collaborative learning in a SPOC environment with proper design, facilitation, and face-to-face interaction groups provided students with opportunities to engage in learning to improve their achievements.