Only open event is the PTA Spring Fayre and then probably an open evening in July. Their are some concerts, have a look at the calendar on the school website. Most Saturday mornings you can wander up the drive and watch sports.
I took my year four boy to the September open evening, we only stayed thirty minutes, looked at the fun stuff displays in Chemistry, Physics, Biology, Technology ( he wants to be a scientist ) he was very keen.
DS2 and his classmates are already talking about secondary schools, one school is very popular in the playground because you get to play golf. I have also used the Reading school history, nearly 900 hundred years old, about the same age as Dr Who