Separating signal from noise: Children's understanding of error and variability in experimental outcomes

A young child eagerly awaits the day when she will pass the 100 cm minimum height requirement for riding on the "thriller" roller coaster at her local amusement park. She regularly measures her height on the large-scale ruler tacked to her closet door. As summer approaches, she asks her parents to measure her every week. A few weeks ago she measured 98 cm, last week 99.5 cm, but today only 99.0 cm. Disappointed and confused, when she gets to school she asks the school nurse to measure her, and is delighted to discover that her height is 100.1 cm. Success at last! But as she anticipates the upcoming annual class excursion to the amusement park, she begins to wonder: what is her real height? And more importantly, what will the measurement at the entrance to the roller coaster reveal? Why are all the measurements different, rather than the same? Because she is a really thoughtful child, she begins to speculate about whether the differences are in the thing being measured (i.e., maybe her height really doesn’t increase monotonically from day to day) or the way it was measured (different people may use different techniques and measurement instruments when determining her height)