It's a great school - I went there for sixth form.
Given that it does not select on 11+ criteria, its results are outstanding.
I would imagine the standard needed is higher due purely on the number of places.
The next criteria is church attendance/involvement - maybe you could consider 'god' and a bit of church cleaning - you wouldn't be the first!!
I also recall they are starting a junior admission - not sure when but I read an article in local paper when visiting my parents who still live there.
Speaking as a Mum in Notts whose son goes to Grantham - do not underestimate travel times. He spends a long while on a bus that is usually late and I end up travelling to and fro for Latin, Rugby, general socialising. My second has just taken the 11+ and the thought of double trips fills me full of dread!