I hope you're still checking this thread - I've only just seen your message.
We live in Harlow and our elder daughter has just got into Chelmsford County High School for Girls and will be starting in September.
As you will have found out by now, there aren't any grammar schools in Harlow (or even any schools with a sixth form). CCHS is the closest one and there is a bus service there from Harlow, but there are other good grammar schools in Essex if you're prepared to move house.
You could try the CSSE website: http://www.csse.org.uk/
Do PM me if you have any questions. We had a really tough time with our primary school - I hope it's easier for you.