The Motivational Climate Scale for Youth Sports (MCSYS) provides an age-appropriate measure of coach-initiated motivational climates in youth sports. Items have a readability level of grade 4.0 or below. Exploratory and confirmatory factor analyses revealed that both child and adolescent athletes (ages 9–14) discriminate between mastery- and ego-involving coaching behaviors. The MCSYS demonstrated acceptable reliability and strong factorial validity. Construct validity research yielded predicted relations within a nomological net that included athletes’ achievement goal orientations, competitive trait anxiety, sport enjoyment and coach evaluations, intrinsic motivation, and self-esteem. In both white middle-class and low income minority samples, the mastery and ego subscales also proved sensitive to a coach intervention designed to promote the establishment of a mastery climate and a reduction of ego climate behaviors. We discuss use of the scale to, measure motivational climate at individual and team levels and the desirability of multi-level statistical analyses of climate data.