You should be able to appeal against the 11+ result itself, but will have to wait for the statutory appeal.
Secondary admissions round â€“ appeals for on-time applications (i.e. those relating to
decisions sent on national offer date) must be heard by 6 July or the next working day, if 6 July falls on a weekend.
In addition to considering oversubscription,
an appeal panel may be asked to consider an appeal where the parents believe that their child did not perform at their best on the day of the entrance test and, as a consequence, did not reach the required academic standard. [Code of Practice]
Before a statutory appeal takes place, some LAs (such as Kent) may conduct an internal review (the "headteacher appeal"). I'm not aware of any other process before the statutory appeal.
Be warned that an internal review may limit your rights at a statutory appeal:
www.elevenplusexams.co.uk/forum/11plus/ ... php?t=5499
(See the section in red, and the subsequent post dated 26th September.)
As far as I know, this was not a problem in Kent last year.