For years I have put pattern blocks in front of my kids only to have them slide all over the place on the block puzzle sheets. I had a DUH moment and finally gave them a magnet board (this could be a cookie sheet) to STICK the puzzle on while they used MAGNETIC pattern blocks
My son explored symmetry in the process. One page asked him to complete patterns "so that the dotted line becomes a Line of Symmetry." You'll see (right) that he made a lovely pattern WITH symmetry, but didn't pay attention to the dotted line/line of symmetry. We had a good discussion about "line of symmetry" and used a ruler to help (below.) This was a nice extension to our symmetry lessons with Magic Mirrors that I'll show you later this week.
Note on materials: I own several different pattern block books: Pattern Block Problems for Primary People