Coagulation is an important process in the context of water purification; and the seed protein of the moringa tree ("Moringa oleifera") is a remarkably effective coagulant. The laboratory course described here is designed to provide high-school students with a stepwise, hands-on experience in investigating the protein-rich coagulant found in "Moringa" seeds. First, the seed powder was applied to model polluted water containing fine clay, food dyes, copper sulfate, and bacteria. This treatment changed the polluted water into clear water via coagulation; all students were convinced that the coagulation-inducing agent was a thermostable cationic protein. Finally, basic biochemical techniques (e.g., chromatographic separation and electrophoresis) were used to show that the target coagulant is a dimeric protein composed of 6.5 and 4.5 kDa subunits. Overall, this made it possible for the students to gain a deeper understanding (more comprehensive than the information taught in formal classes) of protein structure and its real-world implications. This stepwise exercise can be applied to research-based learning programs in high school, as it is an effective learning tool.