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.
But when he was about three-and-a-half months old, the routine fell apart. “I would feed him, but he wouldn’t be asleep at the end of the feed,” recalls Welk. “I would rock him until he fell asleep and put him down, and then he would wake up 30 minutes later and I would do it all over again.” Desperate for some rest, Welk brought Greyson into bed with her, but then she ended up just lying still, holding a pacifier in his mouth all night long. “I didn’t know anything about sleep,” says Welk. “I didn’t know you couldn’t just rock them to sleep and then put them down.”