Recent research has documented well the importance of mastery motivation in early childhood. Thus, it is important to have valid and reliable instruments to measure this concept. The Dimensions of Mastery Questionnaires (DMQ 17) has been used extensively in Hungary and around the world to assess children's mastery motivation from ratings by parents, teachers, and school-age children themselves. Based on empirical and theoretical feedback, a revised version of the questionnaire (DMQ 18) was developed in English, Hungarian, Chinese and Spanish. The aim of the present study was to report and evaluate the psychometric properties of DMQ 18. In this first publication about the new DMQ, 211 3-6 year-old Hungarian kindergarten children's mastery motivation was rated by their teachers, using DMQ 18. Validity was supported by a factor analysis which fit well the theoretical dimensions and by strong correlations between DMQ 18 and the extensively validated DMQ 17 scales. Good internal consistency, interrater reliability, test-retest reliability, and longer-term stability also support the usefulness of DMQ 18. We also discuss the importance and usefulness of measuring mastery motivation in preschool and school age children.ERIC keywords: motivation, early childhood, psychometrics Additional keywords: mastery motivation, questionnaire, teachers' ratings, reliability, validity 2 The US National Academy of Science report, From Neurons to Neighborhoods (Shonkoff & Phillips, 2000), identified mastery motivation as the intrinsic drive to explore and master one's environment, and said it is a key developmental concept, which should be included as part of a child's evaluation. Mastery motivation has two major aspects: instrumental and expressive (Barrett & Morgan, 1995).The instrumental aspect motivates a person to attempt, in a focused and persistent manner, to solve a problem or master a skill or task, which is at least moderately challenging for him or her (Morgan, Harmon and Maslin-Cole 1990). The expressive aspect of mastery motivation produces affective reactions while the person is working at such a task or just after completing it. This affect may or may not be overtly expressed and may assume different forms in different children as the child develops (Barrett and Morgan, 1995).The Dimensions of Mastery Questionnaire (DMQ) is one of several measurement techniques, including challenging structured tasks and semi-structured play, developed to assess mastery motivation (Busch-Rossnagel & Morgan, 2013). The DMQ assesses mastery motivation by having a parent or teacher rate their perceptions of the child's behavior (or school-aged children rate their own behavior) in mastery contexts. This article is based primarily on data from DMQ 18 ratings by teachers of the mastery motivation and competence of Hungarian preschool children. The development of the DMQ scales is briefly described in the next section, followed by previous research on reliability and validity and by cultural comparisons of DMQ results from Hungary, Chin...