This study describes how students' intuitions about sampling are informed by extended experiences in investigating local ecosystems. Elementary students in a rural/suburban district in the upper midwest spent a year conducting first-hand comparative field studies of nearby ponds, prairies, and forests. At the close of the term, we conducted task-based interviews with 26 students at Grades 1/2, 3, and 6 to explore their understanding of the nature and role of samples, particular forms of sampling practices in the field, and the ways in which samples and sampling practices influenced their knowledge about ecosystems. Interviews, which lasted from 60-90 minutes each, were conducted individually. Interviews were designed to address parallel topics at each grade level, although questions were couched in the specific ecosystems investigated by students at their respective grades. Across grades, interview responses reflected transitions in students' understanding of: the concept of a sample, ways to construct a sample, potential sources of sample bias, roles of cause and chance in explaining variability in a sample, ideas about growing sample size, and how to coordinate sample representativeness and sampling variability