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COPYRIGHTED MATERIAL 2 STEM Learning Centers Mina attached a small plastic ramp, backed with Velcro, to a felt board that was mounted to the wall in the class’s STEM learning center. She placed a plastic ball on the ramp and watched as it rolled down the incline and dropped into a tub below. Next, Mina added a second ramp, placed directly be- neath the first ramp, to the felt board. This time, as she again rolled the ball down the top ramp, Mina noticed that the ball completely missed the ramp below it. Carefully, Mina adjusted the lower ramp so that it extended beyond the top ramp. When she rolled the ball for a third time, it dropped off the top ramp, landed in the middle of the lower ramp, and rolled down it before dropping into the tub. “That’s neat,” said Mina’s friend Zach, who had approached the STEM area and was watching. “I know a way to make the ball go the other way, like in this picture.” Zach pointed to a photograph of a street that zigzagged down a hill. “How?” asked Mina. Zach removed Mina’s bottom ramp and repositioned it so that the downward slope slanted in the opposite direction. When Zach rolled the ball down the top ramp, it dropped onto the bottom ramp and rolled the opposite direction before falling into the tub. Mina and Zach continued experimenting with the ramps until they could make the ball change directions several times on its downward course. • • • T he STEM center in this vignette is de- scribed in Activity 2.2 of this chapter. At first glance, it looks like an interesting sci- ence center that allows children to experiment with the properties of inclines. But in this case, the teacher has also planned the center so that children can experiment with the geometric con- cepts of positioning, directionality, and angle. The photograph of Lombard Street in San Fran- cisco, often called the “Crookedest Street in the World” because of its hairpin turns, was deliber- ately added to the center to encourage children to model its pattern of directional change in their own experiments. After the children have had a week to freely explore the effects of directional change and po- sitioning, the teacher plans to introduce a dif- ferent concept. She will encourage children to construct two kinds of inclines, those that are al- most parallel to the ground, and therefore have a very gradual slope, and others that are steep. The children can then compare the speed of cars rolling down them. To more accurately measure the speed of the cars, the teacher plans to help the children count the clicks on a metronome as the cars roll down the slopes. (A metronome is a device used in music to help musicians main- tain a steady beat or tempo.) The use of a timing device integrates technology into the center. It also focuses on quantification as a component COPYRIGHTED MATERIAL 15