You have to teach the difference between the present perfect and the present perfect progressive.
Which of the following would you turn to, in what approximate order?
- A good grammar reference book
- Your "Favourites" (aka "Bookmarks")
- A second grammar reference book
- CeltaStars (our email support group)
- The notes in your Teacher's Book
- A second search engine (eg. Yahoo or MSN…)
- A colleague or tutor
- Something that might be in your mailbox
- A directory or portal
- A news aggregator (which uses RSS)
- Something else…
In the hand-out for the session, I provided further notes on the above, and in the "comments" (see below), I've suggested my own answer.