Over the last three decades, the study of test preparation and test washback has emerged as an indispensable area of inquiry in language assessment. Yet, how test takers' motivation and perceptions of test design and content might mediate test preparation has not been given sufficient attention. Taking the general English module of a high stakes university admission test as its focus, this study explored how test takers' motivation and perceptions of test uses and design are related to their test preparation practices. To this end, 110 test takers responded to two questionnaires: one on test takers' motivation and perceptions, and the other on their preparation practices. The collected data were analysed using partial least squares structural "equation modeling" (PLSSEM) to assess the postulated washback models, informed by "expectancy value" (EV) motivation theory. It was found that positive perceptions of test content were associated with more intensive test preparation. Also, test takers' perceptions of test uses were found to be related to the value they placed on test taking. By contrast, perceptions of test uses and test value did not significantly contribute to test preparation. In general, a test washback model with direct paths from test takers' perceptions to test preparation appeared to account for more variation in test preparation than one without such direct paths. Findings imply that given the complexity of test preparation and washback, theories of motivation must be complemented by broader social considerations to explain test preparation and test washback.