Developmental transitions are experienced throughout the life-span and necessitate adapting to significant and unpredictable changes (Heckhausen et al., 2010; Perry, 2003). The shift from high school to university in young adulthood serves as an exemplar of how these challenging junctures can undermine motivation and well-being. Recent evidence suggests that most (85%) young adults making this transition feel overwhelmed, half (50%) experience immense anxiety (ACHA, 2012), and more than one quarter (28%) withdraw from their institutions by the end of their first year (Snyder & Dillow, 2013). The present dissertation was designed to counter these developments by conducting a systematic analysis of whether motivation-focused thinking (selective secondary control) sustained young adults’ goal striving, goal attainment, and well-being based on propositions stemming from the motivational theory of life-span development (Heckhausen et al., 2010). Study 1 comprised a seven-month field study and showed that motivation-focused selective secondary control striving positively predicted young adults use of behavior-focused selective primary control strategies, which in turn influenced academic performance. Study 2 was based on a seven-month field study and built on Study 1 by demonstrating that increasing selective secondary control striving was related to lower levels of depressive and stress-related physical symptoms for young adults with low high school grades. These effects were mediated by theoretically-derived mechanisms involving selective primary control and discrete emotions. Building on the preceding studies, Study 3 involved a seven-month, pre-post, field design and showed that students with low high school grades and high perceived control who received a motivation-enhancing selective secondary control treatment attained year-end course grades that were 8% higher than their no-treatment peers (74.85% vs. 66.68%). Consistent with theory, treatment effects were mediated by selective secondary and primary control strategies and emotions. Findings from these studies advance the literature by documenting previously unexplored antecedents, consequences, mediators, moderators, and manipulations (treatment) of selective secondary control for young adults in the midst of a challenging life course transition. / October 2016