Understanding how the leading and lagging strands of DNA are synthesized differently can be difficult, even after seeing many animations and videos. I believe that by physically modeling things, students gain a more thorough understanding of abstract concepts; by modeling DNA replication on the floor using shoe prints and markers, students "walk" through the process of DNA replication and become better acquainted with the process.
This is an idea I saw posted on a blog (http://hybridteareflections.tumblr.com/), but all that was available was a simple explanation and a picture. I wrote up illustrated, step-by-step instructions to make this activity clear and easy to understand.
This activity is best done in groups of 7, but you can accommodate smaller groups by doubling jobs (I did it with a group of 8, but larger than that would be a problem and lead to a lot of standing around). It might also be good to have the original DNA molecules (the first part) ready to go so all you have to do in class is replicate it. However, I did not have the extra time to make up the starting DNA myself, so I just had students do it (and we had enough class time, so it worked out well).
Two analysis questions wrap up the modeling, plus you can have a discussion with your group(s) about the process.
I could definitely tell that the modeling helped clear up the process for my AP Bio kids!