Science teachers tend to focus on schemas rather than underlying structures with greater explanatory power. One such structure is the recognition that the logical statement implication can only be falsified. After instruction with a modified version of the four-card hypothesis testing task, a grup of 48 preservice elementary teachers were significantly more able to interpret logical statements, and falsifiers were more successful than verifiers. This study demonstrates that appropriate instruction can lead preservice teachers to understand the process of hypothesis formation and falsification that is the procedure of theory testing in science. (19 references) (Author)