"Most of my seventh grade students hadn't grown much of anything before," reported Naif Shahady, from Slidell, LA. "I wanted them to try some growing and to think about the basic needs of plants."
Early in the year, Naif issued three bean seeds to each student and challenged them to see who could grow the biggest plant (by mass) in six weeks. He controlled the size of the pot and volume of soil, but suggested that students would have to determine what other factors would affect their plants' growth. Students suggested variables such as soil type, type and amount of light, water types and quantities, and fertilizer types and quantities, then took home their seeds and pots and planned their strategies. They were required to keep a journal with pertinent data including observations, measurements, coloration, and their reasoning behind making various decisions about caring for plants.
"Students tended to treat all three plants differently, changing different variables and testing out a range of ideas about what would spur growth," reports Naif. After six weeks, each student brought in their "best" plant and its data table for final judging. Some were so close in size, reports Naif, that students had to weigh them to determine mass. A few, he says, even admitted watering plants just before coming in, hoping the weight would increase!
After reviewing individual graphs and journals to begin to make sense of their data, the class created a class chart to narrow down certain factors that seemed to be significant to producing the biggest plants. Students began to recognize, reports Naif, that they could not draw confident conclusions since there were so many variables involved. "This prompted a discussion about how we could extend our work and set up more controlled investigations to make more accurate conclusions," he notes.