The idea behind extinction (or full extinction to differentiate it from graduated extinction) is that you want to extinguish the behaviour (crying) by not responding to it. As with the check-and-console method, go through your bedtime routine, put them in their crib awake, say good night and walk out. This is certainly the most controversial sleep-training method, and even experts disagree on what you should do next—it all depends on what stage your baby is at developmentally, as well as what works for the parents.
This is considered a ‘cry’ method of sleep training. This technique entails allowing your baby to cry while checking on him at intervals. The goal here is to reassure him every so often that you are nearby and to reassure yourself that he is okay. When you go to check on your baby, you are not “supposed” to pick him up nor engage him much, but simply reassure him using your voice and a loving pat for 2-3 minutes, tops (watch the clock!). With this sleep training method, the goal is NOT to help baby fall asleep – that is what he is learning to do on his own! Instead, the idea is that he falls asleep on his own, in the same “environment” in which he will awaken periodically throughout the night. The knowledge of how to fall asleep unassisted at bedtime will pave the way for him/her to go BACK to sleep throughout the night. Over time, you gradually increase the amount of time between your ‘checks’. See a more detailed step-by-step explanation of this method here: The Ferber Method
It’s okay if you’re not ready. You aren’t missing out on sleep training if you skip it at 4 months: You truly can start sleep training at any age, even in the toddler years, although experts say it’s smart to be aware of developmental milestones and adjust baby’s sleep schedule accordingly. For example, the week baby learns to walk may be tough to implement a sleep-training schedule, and even a sleep-trained baby may see a regression simply because he’s going through such a developmental shift.
If your baby is older than six months, don’t worry, McGinn says: “It’s never too late to develop good sleep habits.” Dickinson says he finds nine months to be a bit of a sweet spot for parents in terms of getting babies to sleep through the night. “They are at a good age for understanding routines and don’t need to eat during the night,” he explains.