Environmental stewardship education, as a locally oriented concept, benefits from being recast to account for the emergent, multidimensional, and interdisciplinary nature of today's most pressing socio-ecological issues. In an effort to infuse environmental stewardship education with global citizenship, instructional materials on community-based conservation in Peru were delivered to high school students in New York, USA. The purpose of this study was to assess the impact of instructional materials on student learning outcomes related to the practice of global citizenship in environmental stewardship education. The CLIA model for powerful learning environments was used to convey the competencies, learning conditions, interventions, and assessments that structured the delivery of the instructional materials. To evaluate learning outcomes, written student responses were analyzed, using the qualitative coding methodology. Additionally, transformative learning was assessed using the Learning Activities Survey. Results suggest a trajectory past knowledge comprehension and toward transformative, empowered action, progressing from a cognitive understanding to affective and ultimately behavioral shifts. Based on these findings, this study conceptualized and operationalized the concept 21st-century stewardship -- a term coined here as an updated stewardship model that is infused with global citizenship's multi-scalar perspectives, global compacts, and layered identities to achieve its maximum impact in our interconnected world.