Your indie school 2 sounds like the one we are applying for, Munch. No information, no past papers
We're also at state primary and DD is the only one applying to indie.
However, this site is v useful for loads of stuff, and has helped me through the preparation. If you can spend some time poking around in all the threads, it'll be helpful to you (even if only for your sanity).
If you search for writing frame, you will find lots of advice on how to structure a piece of writing. This is particularly useful for the shorter writing task. The get your DS to practice this. Give him any topic and give him 20 minutes. Tell him you want to see both a plan and the piece of writing. The plan bit will help you help him see how to improve next time. In one of DD's early writing tasks she did an excellent plan, then compeltely disregarded it when it came to the writing. We've worked on that!
Also there was a really good thread about collecting standard phrases that can be tailored for use in any given situation (e.g to describe feelings, landscapes, colours, textures, etc). Can't remember what the topic header was, maybe someone else can remind us. Point being, have a few prepared which can be thrown into any piece of writing.
We've also just done 2010 SATS papers, which include 2 writing tasks, and I've used the mark scheme to help DD improve her writing. It's very detailed and gives pointers to what SATS markers are looking for. Might not be the same for the indies, but it's a useful exercise. You can get them through a google search.
One other point, handwriting could be important. We had a home visit as part of our application, and I showed them one of DD's projects from school. They were disappointed to see that it had all been done on the computer, and asked if there was anything I had that had been handwritten. Not sure if that will be important in the test, but we've been working on improving handwriting (last May it was only liegible to me, now friends can also read it