The purpose of the study was to validate a writing motivation questionnaire that consists of four scales for first-year college writers including students with low writing skills in basic writing classes and students in typical first-year composition (FYC), to investigate differences between these two groups and to examine the relationship of motivational constructs with writing quality. Participants were 371 college students (142 in basic writing classes and 229 in FYC). Students completed a 49-item motivation questionnaire with scales for goal-orientation, self-efficacy, beliefs, and affect about writing and wrote an argumentative essay. Confirmatory factor analysis provided evidence for the structural construct validity of all scales for both groups. Statistically significant differences between basic writers and FYC students were found on self-efficacy for grammar and strategies and on beliefs about the importance of substance and mechanics. Structural equation modeling found statistically significant positive relationships of essay quality with all three self-efficacy scales and belief about the importance of substance to good writing, as well as negative relationships with avoidance goal orientation and belief in the importance of mechanics. Limitations and implications for motivation and instruction of basic writing students and of adults with learning disabilities are discussed.