i will tell you waht i know but its not much. My friends dd was at st catherines and took the 13plus, which i think is similar but a year late. My friend had to check with the teachers that she was at the right curriculem levels before her dd could take the test. She was- though one of her subjects was very borderline. she was allowed to take the test and passed. However she had set her heart on bexley grammar which was full. My friend appealed but was unlucky so her dd went on the waiting list and finally got a place starting year 10 - she is still there - doing her final year now.
I would ring the council and ask them some details,