I went to a very good Catholic elementary school, one run primarily by priests trained by Jesuits. The priests commonly visited classes, and anything could be interrupted to have an impromptu theological or philosophical discussion. The classes encouraged questioning and doubt in all areas of study. We actually read philosophers such as Plato, Descartes, and Aquinas in the later years.

While I doubt that every child who went through this experience with me came out an ardent seeker of truth, I nonetheless believe this had a huge impact on who I'd become. Also, I should note that I've heard most Catholic schools aren't this awesome.