The Skeptoid podcasts, produced and presented by Brian Dunning from Skeptoid.com, offer simple, interesting, and compact lessons on scientific and critical thinking.
Students should have regular compulsory exposure to good science and critical thinking and Skeptoid could provide one tranche of this exposure. Mythbusters, How Stuff Works, and all the David Attenborough Discovery documentaries could be added to provide an excellent and entertaining overview of the scientific method in action.
Skeptoid episodes typically last around 10 minutes and could easily be broadcast over existing PA systems to all students as part of a short morning discussion session. Home room teachers can then discuss the issues, science and critical thinking covered in the episode.