The goal of this paper is to examine the relationship of student motivation and achievement in low-stakes assessment contexts. Using Pearson product-moment correlations and hierarchical linear regression modelling to analyse data on 794 tertiary students who undertook a low-stakes engineering mechanics assessment (along with the questionnaire of current motivation and the "Effort Thermometer"), we find that different measures of student motivation (effort, interest, sense of challenge, expectancy of success and anxiety to fail) showed atypical correlation patterns. The nature of the correlations further varies depending on the type of test booklet used by students. The difficulty of the early items in the assessment were positively correlated with "anxiety" and "success", but negatively correlated with "interest". In the light of our findings, we suggest that future research should systematically explore (taking into account testing conditions like test booklet design and test-item format) the implications of student motivation for achievement in low-stakes assessment contexts. Until the consequences of these processes are better understood, the validity of assessment data generated in low-stake conditions in the higher education sector will continue to be questioned. With a greater understanding of these processes, steps could be taken to correct for student motivation in such settings, thus increasing the utility of such assessments.