Symmetry can be a difficult and abstract concept for some kids, especially in the upper grades when questions get more complex as well as the shapes they are analyzing. I've found that the easiest way to help students "see" symmetry is by using a mirror. Of course, cutting out shapes and folding and manipulating them is always the first step in the process. But, what happens when the shape or picture can't be cut out and the student still hasn't mastered the concept? This is where the handy-dandy mirror comes in!
I stumbled upon a class set of mirrors a few years back in our science supplies and they have been a life saver during my fourth grade symmetry unit each year. So much so that my students ask for the mirror at the beginning of the lesson and even keep one in their pencil boxes to use throughout the unit. Here is an example of how it works:
Let the students know that in order for the shape or picture to have symmetry, what you see in the mirror should be the exact same as what is on the paper. (*Note- I always reference this first because I've come across a lot of students who have the misconception that if what they see in the mirror is the same as that half of the picture on the paper, it has symmetry. If that were the case, everything they placed the mirror down on would have symmetry!)
I usually start with having them place the mirror horizontally and vertically down on the shape. If it has symmetry, they use the edge of the mirror to trace that line (using it as a ruler). After they have tried horizontal and vertical, we discuss the fact that objects can also have diagonal lines of symmetry as well. Sometimes they tend to skip over this! When they have found all of their lines of symmetry, they are done! It's so simple and it seems like common sense yet many teachers don't use this tool. After using the mirrors for a few days/weeks/lesson most students don't need them any longer because they can finally "see" the symmetry!
I've created some task cards that work great with this skill. You can find them in my Teachers Pay Teachers store. They've really helped my fourth graders to master this sometimes difficult skill. Enjoy!