I think if you are coming from a small school, you had better have some impressive stats outside yards per carry or number of tackles. Size, speed, strength had better be impressive.
When you come out of a big school, you have already competed with a bunch of kids to get a starting job, and the competition you competed with had done the same. An all state running back out of a high school with 2000 kids and an 8 yd/att avg is a whole lot more impressive than one doing the same thing at a high school with 200 (or 20?) kids.
I can remember very well the recruiting process. If you have size, speed, and strength, and your coach is connected and committed to your success AT ALL, you will get attention from recruiters, even at a small school. If you are missing any one of these three pieces, you will struggle to even get return phone calls, regardless of your performance on the field. Big schools are looking for raw material out of high school, not finished product. Atheletes they can mold and make into what they want. Game stats will get recruiters to look at your size, speed, and strength, little more.
All that said, I love a story of any kid being overlooked and beating the odds and doing well at the next level. It's not easy.