I'm from a comprehensive. Had absolutely eff all support applying, my school wanted to charge me to sit the HAT as presumably I was the first person to have done it and they didn't have a clue about it. Although to be fair a group of us went up the open day in June, but that was only because it coincided with a trip to London so we "called in" on the way back.
Weird thing is I don't regret anything or wish I'd had extra support, I've reached the interview stage (which incidentally were the first interviews I'd ever done in my life- no preparation) and I was really pleased with them and enjoyed the experience. The interviewers seemed pretty interested in how I was taught in school too, class sizes, teaching style, etc. I certainly won't be losing any sleep if I don't get in and I won't be blaming my school.