In this prospective study, we recruited a sample of Belgian adolescents (N = 886) to investigate to what extent perceived teachers' motivating style relates to quality of motivation in the beginning of the school year and, in turn, changes in study effort and procrastination by the end of the school year. After controlling for initial levels of study effort and procrastination and for a shared variance due to classroom membership, we found, through path analysis, perceived autonomy support and structure to relate positively to autonomous motivation, which in turn predicted increased study effort and decreased procrastination at the end of the school year. The findings are discussed from a theoretical and practical standpoint.