Background: Uganda's youth development sector faces a persistent challenge wherein substantial investments in skills training, financial access, and entrepreneurship support yield limited productivity outcomes, with youth unemployment rates around 13.3% and underemployment affecting 40% despite numerous interventions. This disconnect suggests conventional resource-based approaches may overlook psychological foundations that determine resource utilization effectiveness. Objective: This study investigated productive mindset as a foundational element in youth development, examining: (1) current mindset orientations among Ugandan youth and their association with productivity indicators, (2) whether productive mindset mediates the relationship between resource access and developmental outcomes, and (3) the effectiveness of targeted mindset cultivation interventions. Methods: A mixed-methods convergent parallel design was conducted from March-September 2024 across five Ugandan districts. The study employed a quasi-experimental design with 420 youth aged 18-30 years (power=80%, α=0.05) randomized to intervention (n=210) or control (n=210) groups. The intervention group received a 12-week structured mindset cultivation program combining cognitive-behavioral techniques, entrepreneurial mindset training, and peer learning, while controls received standard vocational training. Results: Baseline assessments revealed Ugandan youth exhibited moderate-to-low productive mindset orientations (self-efficacy: 22.2±5.7/40; locus of control: 11.4±4.2/23; growth mindset: 3.4±1.2/6). Correlation analyses showed all mindset dimensions significantly predicted productivity outcomes, with self-efficacy demonstrating the strongest association (r=.61, p