Timing is everything. No matter what method of sleep training you use, it is more likely to succeed at particular developmental stages, and more likely to fail at others. The vast majority of children follow a predictable developmental schedule of emotional and cognitive changes in the first 5 years of life.
The best times for sleep training are neither early nor late. Many people assume that getting sleep training over with before the child gets too clever or too entrenched in nighttime habits is the best approach. Others assume that waiting until the attachment bond is strong and/or kids are more independent is important. Both are wrong. The best stages to sleep-train follow a pendulum swing from one age to the next, with difficult periods interspersed between periods of relative ease.
Stages that make it harder to sleep-train are those of heightened emotional vulnerability. In these predictable periods, your child will be more dependent, vulnerable, or prone to separation distress, jealousy or shame.
Stages that make it easier to sleep-train are when your child is less emotionally sensitive. These are periods when the infant or child is more interested in the nonsocial world of objects, actions, and locomotion, and less concerned with other people.
Most sleep-training methods are equally effective. There are at least half a dozen popular sleep-training methods, ranging from "cry it out" to "gentle no-cry solutions." None have been proven more effective than another so pick something that feels right for you. That means go with a method that seems to match your parenting philosophy or approach in general. Ultimately, you have to live with your parenting choices and you know your child best.
There are some ages at which particular methods are likely to work better than others. If you understand the emotional vulnerabilities and strengths that characterize each developmental stage, you will be better equipped to match a sleep-training method with your child’s age.
Pick a method you know you can stick with. That means apply the method consistently, and do so for at least a week.
Things often get worse before they get better. Children already have sleep habits when we decide to sleep train them. Breaking those habits may involve some disruption, disorganization, or outright rebellion on the part of your baby or toddler. As a result your child may sleep less or wake more frequently before she settles into a new routine.
Sleep training is often not a one-shot deal. Even after your child learns to sleep through the night, sleep setbacks can occur at (predictably) difficult ages, requiring parents to think about what's different and how to re-implement effective sleep training.
A family that is getting enough sleep, is a happy, healthy family. Mothers in particular often feel guilty about sleep training because of messages from the media, friends and family (including fellow mothers, unfortunately) that their first and only priority should be their child’s happiness. Parents who are considering sleep training for reasons beyond just the well-being of their child (gasp!) are not only perfectly normal, but are doing the right thing. A sleep-deprived child is a cranky, inattentive one who will have a tougher time learning and socializing. A sleep-deprived parent is often irritable, angry, depressed and ineffective. A well-rested mother and a well-rested child will both be happier, healthier, more alert and more affectionate.