What do you do when you want to get your Stage 3 students authentically and enthusiastically engaged in the active construction of their understanding and fluency with measurement, data collection, representation and interpretation? How do you enable them to make choices about their learning, to measure with purpose, to record and organise the data they produce, to plot the points and to understand that the emerging line tells a story about something real, something changing. Here's one way to approach all of these objectives in an integrative and motivational context. Mark Roddy and Kat Behrend suggest "Calling in the Grow Beast!" The "Grow Beast" is a small, inexpensive, readily available toy that, when placed in water, absorbs it and thus "grows" over the course of several days, and then gradually shrinks to more or less its original size when removed from the water. The object for student learning was the development of skill and understanding in three related content areas: First, through iterative experience, their understanding of the overarching idea that mathematics may be used to analyse, represent, and predict change; second, students will develop their fluency with measurement; and third, students will learn about the use of graphs as a means of representation, analysis, and communication in mathematics. Roddy and Behrend concluded that the evidence provided in their work showed that students were successfully engaged in the development of understanding and skill; Students learned something about the use of mathematics to analyse, represent and predict change; and finally the students developed their skill with measurement, with the use of data and graphs, and communication.