This past Shabbat, I presented a shiur locally on the topic of the “Four Sons” of the Pesach Hagadah.
It’s based on an article by Rav Amnon Bazak of Yeshivat Har Etzion. The article can be found at http://www.vbm-torah.org/pesach/pes68-ab.htm and my source sheet at http://ravron.files.wordpress.com/2013/03/another-look.pdf