Here is David Crystal on It’s Only a Theory from BBC4. It’s on YouTube so obviously (sigh) you won’t be able to see it in school, but it’s only 10 minutes or so and well worth a look for ENGB1 – Language & Technology and ENGB3 – Language Change:
Don’t forget to read David Crystal’s blog, too: http://david-crystal.blogspot.com/
It’s on the Edmodo RSS feed of course, for those in my English Language A-level classes, but for arming yourself with good arguments and examples purposes you may like to have a look through some past entries, along with those from the brilliant (and A-level focused) English Languag @ SFX which is probably more useful than any text book (including the one its author wrote) or revision guide.
Heald English 