This study examined the factorial and construct validity of a multi-dimensional measure of motives for writing with middle school students. The Writing Motivation Questionnaire included 28 items assessing seven motives for writing. Two motives assessed intrinsic reasons for writing (curiosity, involvement); three motives addressed extrinsic reasons (grades, competition, and social recognition); and two motives apprised self-regulatory reasons (relief from boredom, emotional regulation). A sample of 1983 sixth- (n = 970) and seventh-grade students (n = 1013) from a school district in the USA completed the questionnaire as well as a District writing test administered at the same time and a State writing test administered eight months later. Confirmatory factor analyses supported the hypothesized seven-facet structure of the Writing Motivation Questionnaire as well as second-order models (e.g., three-order factor involving intrinsic, extrinsic, and self-regulatory motives). Measurement invariance was established for grade-level (sixth- vs. seventh), gender, free/reduced lunch status, special education status, and race (White and non-White students). All seven writing motives evidenced adequate reliability for research purposes. Students' writing motive scores predicted writing performance on the District and State tests. Recommendations for future research are provided.