The nature of the quantities involved in arithmetic problems promotes semantic encodings that affect the strategy chosen to solve them (Gamo, Sander, & Richard, 2010). Such encoding effects might prevent positive transfer to problems sharing the same formal mathematical structure (Bassok, Wu, & Olseth, 1995). In this study with 5th and 6th graders, we investigated the conditions promoting positive and negative transfer in arithmetic problems that could be solved with two distinct strategies. We showed that basic training do not overcome the initial impact of semantic encodings, and we provided evidence that a poor semantic encoding of the training problems leads to transfer errors. This suggests the existence of ontological restrictions on the representation mechanisms involved in word arithmetic problem solving.