Adolescents spend one-quarter of their waking hours alone, yet the significance of this time is little understood. This study evaluates developmental changes in the experience of solitude between late childhood and early adolescence. Four hundred eighty-three European American fifth through ninth graders provided experience-sampling reports on their companionship and subjective states at random times over a week. The findings show, first, that time alone becomes more voluntary across this age period. Second, time-series analysis shows that for seventh through ninth graders, but not fifth and sixth graders, solitude had a positive after effect on emotional state. Third, adolescents, but not preadolescents, who spent an intermediate amount of their time alone were better adjusted than those who spent little or a great deal of time alone. As a whole, the findings suggest that, while continuing to be a lonely time, in early adolescence solitude comes to have a more constructive role in daily life as a strategic retreat that complements social experience.