It is a pay on the gate and then wander around the activities as you wish event. Very informal, I will be taking my year 4 boy as part of his brainwashing.
You can also go to,
Open Days 2009
Thursday 2 July, Wednesday 23 September, Thursday 24 September
4.15 - 5.30 Walk/Tour of School
5.30 - 6.30 Talk/Question and Answer session
My DS2 liked the science labs, the interesting experiments and displays. I would suggest skipping the Talk bit until year six. The more they are familiar with the school the less daunting and more exciting it becomes.