L2 prepositions are traditionally taught in a non-explanatory manner by having students learn each use individually. This study examines the effectiveness of an alternative explanatory approach based on cognitive linguistics, which considers the multiple uses of a preposition as related. Consequently, learners can be shown a general schema that underlies all the uses, as opposed to treating them as unrelated items. Two groups of intermediate-level university Spanish learners were taught the prepositions "por" and "para" using a cognitive linguistic description, while a comparison group was given a list of the different uses as individual items to memorise. Although both groups increased in their accuracy of response to a fill-in-the-blank and a multiple-choice task following instruction, the experimental groups were able to maintain or improve their performance on the delayed post-test, while the comparison group decreased significantly in accuracy. The experimental groups were also more certain about the accuracy of their answers and were less likely to confuse "por" and "para" in free writing. Factors that may have influenced the results include the content and delivery method of the treatment, learner cognitive styles and problems with applying cognitive linguistic models of prepositions to language pedagogy. (Contains 7 tables and 2 figures.)