4 kids so far here. If you mean training to sleep independently through the night in their own room -- we wait until they are good and easy and don't really need to nurse any more (other than comfort nursing). Then they move to their own room and I sleep in that room with them without my wife. I'm a heavy sleeper. If they cry enough to really wake me up, I comfort them for a bit. Mostly I sleep through their crying. Within about three days to a week, there is zero crying at night and I move back to the bedroom and we use a baby monitor.

It has worked like a charm 4 times straight, but your mileage may vary.

Other sleep tips, as they get older:

- No reading in bed near bedtime, ever.

- No playing in bed near bedtime.

- No nighttime routines except short short hugs and kisses. No tucking in.

- Train them to put their pajamas on by themselves and brush their teeth by themselves as soon as they are physically able to do those things, and make sure they do it without help each night.

- No toys in the rooms except stuffed animals and similar bedtime items.

- If they get in the habit of calling for you unnecessarily at night, start taking stuff away each time you come (e.g., their least favorite stuffed animal). That alters the risk/reward ratio for them and they'll stop calling for you for no reason very quickly.