Being told procedures and concepts before problem solving can inadvertently undermine the learning of deep structures in physics. If students do not learn the underlying structure of physical phenomena, they will exhibit poor transfer. Two studies on teaching physics to adolescents compared the effects of "telling" students before and after problem solving. In Experiment 1 (N = 128), students in a tell-and-practice condition were told the relevant concepts and formulas (e.g., density) before practicing on a set of contrasting cases for each lesson. Students in an invent-with-contrasting-cases (ICC) condition had to invent formulas using the same cases and were told only afterward. Both groups exhibited equal proficiency at using the formulas on word problems. However, ICC students better learned the ratio structure of the physical phenomena and transferred more frequently to semantically unrelated topics that also had a ratio structure (e.g., spring constant). Experiment 2 (N = 120) clarified the sources of the effects while showing that ICC benefited both low- and high-achieving students. (Contains 7 figures, 1 table and 2 footnotes.)