When to start sleep training: At least six months, research says

Macall Gordon, M.A.
Sep 10
5 min read

Updated: Nov 17

If you’re a parent running on fumes, you’ve probably typed “when to start sleep training” into Google at 2 a.m. and found conflicting advice. Most books insist you can start sleep training at 3–4 months or even earlier.

The surprising truth? There’s no research showing any benefit to sleep training before six months, and plenty of reasons to wait.

Let’s break down the science, the myths, and what this means for your family.

What the research says about early sleep training

Parents often assume there must be studies backing up the advice to begin at 3 or 4 months. But when you dig into the research, here’s what you find:

Almost all studies on sleep training methods (like the Ferber method or extinction) were conducted with babies six months and older.
The few studies done on younger infants weren’t actually “sleep training.” They often were a package of strategies that may have included some instructions about slight delays in responding or using “drowsy but awake.” Only one study exists that used the Ferber method on a group of infants under six months.
Studies that tried to prevent sleep problems in younger babies found only tiny improvements that didn’t actually last.
The notion that it will be “harder if you wait” has never been studied.

So, we actually know very little about using sleep training strategies on infants under six months. If you can wait, babies are developmentally more ready and we actually have more research to back that up.

Why six months matters

There are big developmental reasons that make six months a turning point in child sleep.

Sleep becomes more organized. At this stage, babies have more predictable sleep cycles with chunkier naps and a reliable early bedtime. They can go longer at night without feeds.
The four-month sleep regression has passed. Those endless night wakings usually calm down, giving you a better baseline.
Babies gain new skills. Six-month motor and cognitive milestones help with self-soothing and make retaining patterns and routines more possible.
They may move to the crib and their own room. It’s often when babies move out of their parents’ room. This can be a great moment to learn new sleep skills: new room, new sleep pattern.

In other words, at six months, your baby has more “infrastructure” for learning to sleep independently. Rather than sleep training being harder if you wait, it can actually be easier and faster.

Why do most books say 3–4 months?

“If the American Academy of Pediatrics and research say six months, why do most books say 3 or 4 months? I’ve seen some places say you can start as early as 8 weeks!”

The claim that “the earlier you start, the easier it will be” sounds convincing to desperate, sleep-deprived parents, but it’s simply made up. No studies have ever investigated this question, not one.

Experts say, “If you don’t start early, habits will become engrained,” but there’s honestly no evidence that this is the case. If you think about it, what does this even mean? That you literally can’t change your child’s behavior? Ever?

It’s possible that the unspoken assumption is that older babies will cry more. Younger babies, they will say don’t know the difference. But what they don’t tell you is that younger babies have fewer skills to manage distress. Crying isn’t a neutral behavior. At younger ages, crying is more costly and it takes less to throw a younger baby’s system off.

Older babies may cry, but they can do things to help themselves calm down. “Self-soothing” is more within reach of older babies. They have cognitive skills and motor skills and attention skills. They also may understand how to lobby for what they want. So, there can be intentionality behind some of their crying. In that way, it’s harder for the parent, but it’s not harder for the child.

Other reasons not to start too early?

Sleep is still developing. Before six months, brain structures are still developing and sleep is a moving target. Many books say to start sleep training at three months right before the four-month regression, a time of massive brain development. Lots of babies sleep great at three months only to start waking again at four months. Why spend all that time sleep training if it’s just going to get erased during the regression?

The younger the baby, the less crying they can handle. Crying and distress are not benign. The younger the baby, the less they can handle without help. The notion that a newborn can be crying hard by themselves and that they’ve “self-soothed” because they fell asleep isn’t exactly true. The younger the baby, the fewer resources they have at their disposal. A 3- or 4-month-old, can barely get their hand to their mouth to suck on it. If they’re crying hard, they can’t even do that. Self-soothing happens when distress is manageable. The younger the baby, the less distress they can handle on their own.

Sleep training tends to overlook feeding issues or needs. Early sleep training tends to underestimate or overlook legitimate feeding needs or issues because of its hyperfocus on behavior. Again, with younger babies, the picture is not so clearcut. Feeding issues are still very prominent in the first part of the first year and not every baby can go long periods without a feed. Books also tend to talk in averages and there’s huge variation between infants in the newborn period. You can’t say what “a generic baby” “should” be able to do at this age.

So, when to start sleep training?

The best answer is: when you decide you’re ready to change your status quo. There is no “too late.” Before six months, focus on building healthy sleep habits and a predictable sleep schedule, but don’t stress about formal methods.

After six months, if things are sustainable and everyone is sleeping fairly well, you don’t have to do anything (I’m serious). If there’s ever a point where you feel like you’re ready to stop [doing that middle of the night feed/laying with your toddler at bedtime/cosleeping at 4am], you can make a change. There literally is no such thing as “too late.”

If you need a roadmap that’s not going to scare you into doing something and will give you some commonsense, supportive strategies, check out, Why Won’t You SLEEP?! A Gamechanging Approach for Exhausted Parents of Nonstop, Super Alert, Big Feeling Kids (also on Audible).