Catalysis with transition-metal complexes is a part of the inorganic chemistry curriculum and a challenging topic for upper-level undergraduate and graduate students. A hands-on teaching aid has been developed for use during conventional lectures to help students understand these catalytic reactions. A unique method of illustrating the coordination polymerization of propylene with interlocking building blocks is described. Three metallocene block models mimicking real catalysts recognize top and bottom faces of a prochiral propylene monomer block model and subsequently provide three polypropylene structures with different tacticity. The monomer recognition processes of the metallocene block models are based on steric hindrance, similar to those of the real catalysts. (Contains 4 figures.)