Greetings all. Though I am away today there are a few additional useful notes here as you begin looking into composition writing.
The GLA12 has two extended responses, the 2nd of which is composition writing. Now, this style of writing is very open-ended. There are no rules in terms of the number of paragraphs and the topics are usually quite broad.
Take a look through the package of sample compositions. Read through it with your table and determine what seems to work well, and what tends to go wrong with this style of writing. Create a list of these items on the board as you read through them.
If you want to see more examples, check out the RESOURCES tab at the top of the page. Under Grade 12 you'll see a link to other sample compositions. There are an additional 6 samples of compositions there.