Math Practice #5: Are number lines and graphs considered tools? Some argue they can be created by tools, but are representations. How would the CC authors respond to this? And please clarify “concrete models”. Thanks!
Yes, number lines and graphs are tools; for that matter, equations are tools. Or, more precisely, they can be tools if students make conscious use of them to solve problems. A concrete model is any physical setup that models a piece of mathematics; that includes manipulatives in elementary school, but could also include things like models of sliced cones used to visualize conics in high school, e.g. Dandelin spheres.