To examine developmental processes, intervention effects, or both, longitudinal studies often aim to include measurement intervals that are equally spaced for all participants. In reality, however, this goal is hardly ever met. Although different approaches have been proposed to deal with this issue, few studies have investigated the potential…

School motivation and attachment typically decline after the transition to middle school. According to the stage-environment fit approach, extracurricular activities are supposed to promote motivation. However, research has shown that the effects depend on the quality of the activities, which usually is measured by assessing students' individual…