Classify two-dimensional figures in a hierarchy based on properties.
Learn the definition of polygon, and start to flesh out a heirarchy of quadrilaterals. Relate to heirarchies in nature. Classification is fundamental to the way humans think, so being comfortable with this concept is very important, not only to the student’s further exploration of math, but to reasoning in general. Here's a video covering all the concepts necessary to introduce polygons.
Notes: The Common Core is too vague. Which properties?