Student agency--the ability to exercise control over one's own thought processes, motivation, and action--is a central skill in today's information age. As technology continues to accelerate learning expectations and change, it is essential that one can make independent decisions, self-regulate, and adapt to complex, changing environments. The World Economic Forum (2023) highlights such skills as "resilience, flexibility, and agility," and "motivation and self-awareness"--key skills associated with student agency--as vital for success in the workforce. This literature review (1) provides a working definition of student agency; (2) describes how student agency develops; (3) discusses specific instructional practices that support the development of student agency; and (4) analyzes how student agency has been assessed. The review concludes with implications for the design and use of student agency assessments in primary and secondary schools.