Project Inquiry-Based Mathematics was a National Science Foundation Math-Science Partnership implemented in a Great Plains city school district with a significant K-12 Native American population. One goal of the project was to reduce the achievement gap between Native American and non-Native students enrolled in district. This gap reduction was to be achieved using inquiry-based mathematics curricula along with cognitively guided instructional strategies, particularly at the elementary level. This study focuses on whether inquiry-based mathematics strategies were consistently implemented in three fifth-grade classrooms at K-5 elementary schools with significant Native American student populations. Test results of Native American students at these three schools are compared with the test results of Native American fifth grade students at a fourth school considered by district leadership to be an exemplar of inquiry-based math instruction. Possible reasons for the performance disparity are explored.