My dd is in year 8 at WGSG. Although their admission policy does award 10% of places to the top Maths scores in the Kent test, this admission criteria comes after the sibling rule has been applied, so with a brother at WGSB a pass will get your dd in. They give any child struggling with Maths extra assistance. My dd's friend - along with quite a few others - struggles with Maths and in year 7 had a 6th form Maths 'buddy', it was very discreet and took place out of the classroom. They are not streamed in Maths until year 8. We also live in Orpington.
Thank you Mystery and Lefol I must admit I did panic when I found out about the specialism.
Wishful, I appreciate your message it is always reassuring to hear from someone who has first hand knowledge.