This research explores the effect of mental model-based learning on understanding school chemistry. The learning activity included group discussion, presentation and class discussion. Pre-service chemistry teachers (PCT) analyzed school chemistry topics in relation to essential underlying concepts. The development of mental models was monitored using a diagnostic test and observations. Most of PCT had two initial models, namely scientifically more accurate ones as in the concept of activation energy and dynamic equilibrium, and incomplete one as in the concept of limiting reagents, enthalpy, reaction speed, collision theory, acidity, chemical reaction, equilibrium constant and titration. PCT's mental models in school chemistry topics experience development with average scores ranging from 39.14 to 64.00. Wilcoxon signed-rank test with the significance level [alpha] = 0.05 shows a significant difference between the median initial and final mental models.