We used this activity while we were learning skip counting by two. I started by explaining to the boys that skip counting by two is like counting pairs of something. Ask how many feet they have? How many hands or eyes? Tell them that having two of something means you have a pair - pair of hands or pair of eyes. We tried to find other pairs around us (shoes, ears, knees...) And that is when I pulled out the socks! We are counting till 20 so I had 10 pairs of socks for them to hang on the clothes line.
Everytime they pined a pair to the line, they would skip count from the beginning all the way to the one they just pinned.
They thought this was such a funny idea ;-)