The integrated STEM activity described in this article incorporated two investigations that sought to develop children's understanding of fair-testing: (1) the first parachutes: how does the angle of a parachute frame affect the speed of descent?; and (2) modern parachutes: how does the size of the parachute canopy affect the speed of descent? This STEM activity was implemented in a third-grade class and a revised version was taught two weeks later to a different third-grade class in the same school. Both classes had a different teacher who lead each of the lessons. Two preservice teachers worked with small groups of four to five children; one facilitated the group activity while the other recorded observations using an "observational protocol" devised for this investigation. The authors share insights into the approaches and pedagogies that supported children's learning and report on how opportunities were built in to develop and assess STEM understanding.