There is an excellent piece in The Economist (HT to Arts & Letters Daily). It examines the debate about the proper role of government in the economy. It does a particularly good job of putting the expansion in to a longer perspective - not just examining the reaction to the recent financial crisis, but providing a more balanced view of the expansion of government, it's power, and the resultant financial burden necessary to support that expansion.
You might want to consider giving it as an auxiliary reading when you discuss the concept with your classes. It's well-written (as so many of the pieces in The Economist are), and I suspect it will provide several points of departure to help students get their arms around the idea.
As always, I look forward to your comments.