With my mares foal a few years back, I just seperated them on two different properties, though not alone. The gelding was with the colt and the mare was with my 2 year old filly at the time.
Though, at my training school I'm attending, they halter break, hot walker break, show prep, wean... all for money. The people come in, drop off the babies in a stall and leave. 2 months later, come back with baby fully weaned, halter broke, and what ever else they want done with them.
So, I wouldn't know a gradual training method, I have no way of doing one. Any I have experienced or done have been sudden weaning.