We constructed the PDEODE (Predict-Discuss-Explain-Observe-Discuss-Explain) teaching strategy, a variant of the classical POE (Predict-Observe-Explain) activity, to promote conceptual change, and investigated its effectiveness on student understanding of the evaporation concept. The sample consisted of 52 first year students in a primary science education department. The students' ideas were revealed by a test consisting of eight questions. The PDEODE teaching strategy was designed on the basis of the students' preconceptions. Conceptual change in students' understanding of evaporation was evaluated by administering the same test as pre-, post and delayed post-test. The test scores were analyzed by both qualitative and quantitative methods. Statistical analysis using general linear model repeated measures of student test scores point to statistically significant differences in pre-, post-, delayed post tests and total scores (p<0.05), suggesting that the strategy helped students to achieve a better conceptual understanding. Further, no statistically significant differences were observed between post- test and delayed post- test scores, suggesting that teaching strategy enabled students to retain their new conceptions in their long-term memory.