GDP is a measure of the aggregate amount of economic activity that takes place within a country's borders in a given time period. It's growth has become the most obsessed over economic statistic there is... therefore we should know more about it and try to understand it's history and weaknesses.
I love listening to a good podcast and the LSE offers talks recorded on iTunes free of charge. Some can be pretty advanced and more difficult to access, but I encourage interested students to try listening to them. The one I link to below is great, and I think offers a wonderful set of arguments for criticising and evaluating GDP. Encourage students to discuss this with their tutor or class as this helps gain some easy credit in the exams!