I was never in a boys-only school; however, during the tenth grade, I was placed in an all boys class for English, Chemistry, and Government because of some idiotic honors program thing. The administration's justification was that it would prevent distractions. I remember feeling much more uncomfortable in the all boys classes than in the mixed-sex classes. Many of the boys were incredibly obnoxious and/or arrogant. It was very intimidating. As far as distractions go, the boys in these classes spent more time "horsing around" than in the normal mixed-sex classes. I did not like it.