Small classes are excluded, so as you say, biased towards private schools. My niece was hit by this but luckily still did well enough to get a place. She was attending a large school in a deprived area. Her coursework was A*, given predicted AAA but was downgraded to ABB.

The minister of education's reason for downgrading the grades was so that pupils did not end up in jobs they were not capable of doing. Delicious irony.