This is an activity that teaches students to classify acute, obtuse, straight and right angles using semaphore flag signals. Why semaphore flag signals? Because they're fun, interesting and "real." And also, they're a good example of how to teach a concept beyond the "prototypes."

What do I mean by this? Well, do an image search on "right angle" and you'll see that the examples that show up are "textbook prototypes." That is, they all have a side resting on the horizontal, the other on the vertical and they all face right, which is the best way to confuse someone into thinking that it is "right" because it faces right (which is not true at all....)

So, by using this activity, your students will understand all the different ways these angles can appear. It also includes detailed instructions on how to teach this using a fun and interactive "discovery" method where students develop the concepts of these angles using "properties" instead of "labels."