This study uses a concurrent embedded mixed-methods design to assess the impact of additional funding on student outcomes in a large, urban school district in the Southeastern United States. The district implemented student-based budgeting (SBB), which allocates dollars to schools based on student characteristics using a weighted student funding (WSF) formula and provides flexibility to principals to allocate those dollars under site-based budgeting. Using simulated instruments in a difference-in-differences framework, we estimate the impact of additional funding on student outcomes provided by WSF. Student test scores in math and ELA increased by 0.14 and 0.12 standard deviations, respectively. Our qualitative analysis suggests that the flexibility given to principals was a key mechanism that improved student outcomes.