C.I.O. is the most famous sleep training technique, and the most controversial — although, despite its daunting name, it is safe and effective. In its simplest form, unmodified extinction, you place your infant down at bedtime, drowsy but awake, and then leave the room, without returning to check on or soothe your baby. This method will work quickly, but often produces prolonged periods of crying for a few nights, which can be difficult for parents to tolerate.

It’s difficult if not impossible to sleep train if you share a bed with your child. There’s good evidence that bed sharing is associated with sleep difficulties in infancy and beyond. One survey of more than 50,000 Norwegian families showed that bed sharing was associated with more frequent night awakenings at both 6 and 18 months. Switching your child to sleeping independently for a week or so prior to sleep training can be helpful as you can soothe your child to sleep in the new sleeping environment first.
Most sleep coaches say the ideal time to start sleep training (or promote independent sleep, not necessarily using the cry-it-out method) is based on your baby’s development, but is usually somewhere between four and six months, when your baby hasn’t had much time to get used to nursing or rocking to sleep. At this stage, most babies are also developmentally ready to learn the skill of falling asleep on their own, explains Jennifer Garden, an occupational therapist who runs Sleepdreams in Vancouver. Around four months of age, some babies go through a sleep regression because their sleep cycles change and there are longer periods of lighter sleep per cycle. “It’s a great time to work on independent sleep skills,” says McGinn. Other babies’ slumber derails around this time because they are working on new skills, like moving around and rolling. Some parents choose to wait until things settle down before embarking on a sleep-training method, but you don’t have to, says McGinn.
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