Introduction to Symmetry

From site:  This site is designed for students and teachers interested in exploring symmetry (grades 7-12). It contains lesson plans, definitions, examples, activities, and links to other web sites. There are also some extension activities for those who would like a little challenge.

Geometry Session 7: Symmetry

From site:  Symmetry is one of the most important ideas in mathematics. There can be symmetry in an algebraic calculation, in a proof, or in a geometric design. It’s such a powerful idea that when it’s used in solving a problem, we say that we exploit the symmetry of the situation. In this session, you will explore geometric versions of symmetry by creating designs and examining their properties.