Three thousand, three hundred and ninety-five families, whose child attended one of 80 different day or resident summer camps for at least one week, completed customized questionnaires that measured growth from precamp to postcamp in four domains: Positive Identity, Social Skills, Physical & Thinking Skills, and Positive Values & Spirituality. Parents, children, and camp staff reported significant positive change in these four domains, more than would be expected by maturation alone. Most gains were maintained or showed additional growth six months later. Few of the camp's structural elements correlated with growth, nor did striking gender, age, or ethnicity differences emerge. The study highlights the particular strengths of camp as an educational institution and social movement and suggests that different variations of summer camp can provide potent developmental experiences.