A popular specialist sixth form academy's Funding Agreement says it's admissions policy should be fair, objective and transparent. It isn't transparent though because they use a complicated combination of aptitude test score, widening participation scoring and interview scoring and the details of how they do it aren't published. There's no way you can tell from the admissions policy what your child's chances are of getting in.
They're not subject to the admissions code, so what, if anything, can parents do about it? Who would they complain to if not the Schools Adjudicator?