Although mastery motivation appears to predict school success, individual assessment of mastery motivation is too time consuming and limits the application of this research. This study examined the psychometric properties of the Dimensions of Mastery Questionnaire (DMQ). The study focused on the validity of the measure for Head Start parents, whether it correlates with individually administered mastery tasks, and the relation of child-rearing practices with child mastery motivation. Participating were 176 Head Start children and their families from 6 rural communities in Colorado. Ten percent of the sample were Hispanic; 31 percent, American Indian; and 53 percent, Anglo. Caregivers completed a battery of questionnaires, including the DMQ, Social Skills Rating System, and three measures of child-rearing practices. The Battelle Screening Inventory was administered, and children were given mastery tasks to assess their goal-oriented mastery behavior and preference for challenge. Findings indicated that mastery motivation can be reliably reported on the DMQ by Head Start parents. The instrument had adequate interrater agreement, internal consistencies, and cross-time stabilities with these parents. The factor structure was somewhat different from the test blueprint, yet was interpretable. There were difficulties documenting the instrument's convergent validity, with the most plausible explanation being that reports of child behavior across different contexts tend not to correspond very well. The DMQ was more strongly related to parent rating of children's cooperation and assertiveness, implying that some of the scales tap an aspect of preschool social competence. (Contains 12 references.) (KB)