This report summarises the research activities and findings from the TLRI-funded project conducted in various schools entitled Building Students’ Inferential Reasoning: Statistics Curriculum Levels 5 and 6. The project was a 2-year collaboration among two statisticians, two researchers and nine teachers. The project team designed innovative approaches to develop students’ informal inferential reasoning and sought evidence that these innovations had a significant effect on improving students’ statistical reasoning in this domain. Key findings Students initially used descriptive approaches to boxplot comparisons and expressed everyday conceptions of sample and population, but later moved towards thinking inferentially. Designed learning trajectories can lead students to “discover” a rational basis for making claims when comparing