That is a good question....anxiously anticipating the consensus.....
my 5 week olds didn't seem to want to climb the ramp I had to get up off the ground at night.....
I found a tree branch about a 1 inch diameter and about 4 feet long that I put one end on the ground and braced the other end in the fence about 2 feet off the ground ......some of them hop up on it and some still do not....
From what I have read on other threads some just know what to do early and some are late bloomers on most all 'chicken behaviors'