We applied latent class analysis and the rule space model to verify the cumulative characteristic of conceptual change by developing a learning progression for buoyancy. For this study, we first abstracted seven attributes of buoyancy and then developed a hypothesized learning progression for buoyancy. A 14-item buoyancy instrument was administered to 1089 8th grade students to verify and refine the learning progression. The results suggest four levels of progression during conceptual change when 8th grade students understand buoyancy. Students at level 0 can only master "Density." When students progress to level 1, they can grasp "Direction," "Identification," "Submerged volume," and "Relative density" on the basis of the prior level. Then, students gradually master "Archimedes' theory" as they reach level 2. The most advanced students can further grasp "Relation with motion" and arrive at level 3. In addition, this four-level learning progression can be accounted for by the Qualitative-Quantitative-Integrative explanatory model.