Discovering the Vertical Line Test

As we are working through my favorite unit of the year, relations and functions, I’m loving the opportunity to pull out my shower curtain coordinate plane.  

I created my coordinate plane using electric tape, duct tape, and a shower curtain from Dollar Tree. It has come in handy for so many different activities!

A few years ago, I made a promise to myself to let my students discover the vertical line test for themselves.  To aid my students in thinking about the what functions look like, I asked my class for a few volunteers.  

First, I asked my students to stand on the coordinate plane so that their bodies formed a function. 

Next, I asked them to stand on the coordinate in such a way that they were NOT a function.  

After repeating this process several times, I asked them what they noticed.  It became pretty clear to them that the points in the non-functions always lied in vertical lines.