Universities get the A level results about a week before students do. They then go through every candidate accepting those with the grades and looking at the near misses until places are full. They do often take lower grades as they then get someone who wanted to go there in the first place but no-one can guarantee this year's picture.
If your 'firm' rejects you then the insurance uni will look at the results and the process is repeated. On results day your child will be able to log into Track and see what has happened [usually they do this before coming into school to get results]; sometimes unis will e-mail as well.
If you are rejected by both unis you get a clearing number and can look at what uni places are still available. If you decide you do not want your firm or insurance then you have to ask to be released into clearing and this can take time.
Hope that helps
