Was Ferber wrong?

_english baby sleep ferber iglowstein naps pantley sears sleep coaching sleep needs sleep training wake windows weissbluth Nov 24, 2020

I compared the recommended amount of sleep and length of wake windows for 9 months old babies in 7 of the best selling baby sleep books on Amazon and in one recent research paper.


Today's question is from Heather:

“Hi, my son will be eight months in two days. What should his wake windows be and how long should each of his naps be? The last few days when he would normally be going down for a nap easy, he has been fighting it. Thanks!”

If you would like to know whether your own child gets enough sleep, click HERE!


Is it a nap transition?

First of all, Heather, I am not sure how many naps your son has – and that is important information to figure out his schedule and why he resists naps. Most children at this age usually have two naps.

Marc Weissbluth conducted a nap survey a few decades ago and he published his results in a scientific paper (1). He is a pediatrician so he asked parents of children who came to his office how many naps their children had. He found that:

  • At 6 months of age: all children napped at least once a day, 84% of children napped twice, and 16% of children napped three times.
  • At 9 months of age: 4% of children napped once, 91% of children napped twice, and 5% of children napped three times.

This means that if your son still naps three times, then the most probable reason for his fussiness during nap time is that he's nearing a nap transition and two naps would be more appropriate for him.

But what if he has already gone through the 3/2 nap transition and already naps twice? In this case, he might resist naps simply because his wake window has increased and he's not sleepy enough at his regular nap time. This could be helped if you adjust his schedule by considering age appropriate wake windows!

What is a wake window?

The wake window is the amount of time a child can comfortably stay awake. Comfortably is a very important word here, because of course, if you don't let a child sleep, they can stay awake for quite a while! But the concept of wake window refers to the amount of time that the child would stay awake in an ideal environment. Other names for this concept (“happily awake span” or “endurable awake hours”) express similar meanings.

If a child naps two times per day, it means that he will have three wake windows during the day: One from morning wake up until the morning nap, the second is from the end of the morning nap until the afternoon nap, and the third is from the end of the afternoon nap until bedtime.

The three wake windows do not have to be exactly the same: some children are more sleepy in the morning, other children are more sleepy in the afternoon and it is absolutely okay if some wake windows are shorter, while others are longer. They could also vary considerably day-to-day, but still, it makes sense to try to find the wake window of average length that would be appropriate for an eight-month-old baby on most days.

What do the best-sellers say?

I looked at 7 of the best-selling books on Amazon about baby sleep and tried to find information in them about wake windows for 8 months old babies.

Two of them (2, 3) were about newborns, so naturally, they did not include this information. The third book, Good night sleep tight from Kim West (4) had some sample schedules for this age, but it did not say how long the naps or the wake windows should be.

The rest of the books included tables about age appropriate information that could help you figure out your schedule. However, you won’t find information for 8-month-old babies in any of these books, because most studies look at children in three months intervals. You will find recommendations for newborns, three-month-old, six-month-old, nine-month-old, and twelve-month-old children, but not for the ages in between. I looked at the recommendations for nine-month-old children which is close enough to your son’s age and I summarized what I have found in the table below.

I included total sleep, nighttime sleep, daytime sleep and wake window length. Where these were not readily available in the books (marked by an asterisk), I calculated them from the information that they did have.

Age (months)
Total sleep (hours)
Nighttime sleep (hours)
Daytime sleep (hours)
Wake window in case of 2 naps (hours)
William and Martha Sears: The Baby Sleep Book (5)
3h 10 min – 3h 20 min*
Elizabeth Pantley: The no-cry sleep solution (6)
Richard Ferber: Solve your child’s sleep problems (7)
typical range: 11.25-13.25
Weissbluth (8)
7-9 or 9
13.6 (7-9 months), but mentions another recent research where 12.9 (6-8 months)
No data
2-4 hours for 93% of children
Mean= 3.1, extremes: 1 and 5.5
Iglowstein (9)
2nd and 98th percentiles: 10.5 and 17.4
2nd and 98th percentiles: 9.2 and 13.3
2nd and 98th percentiles: 0.2 and 5.3
Calculated for the 2nd and 98th percentiles: 2.2 and 4.5


If you would like to know whether your own child gets enough sleep, click HERE!

You can see that the first two books in the table (The baby sleep book from William and Martha Sears, and The no-cry sleep solution from Elizabeth Pantley) has quite similar, or at least overlapping values: 14-14.5 total sleep, 11-12 hours of nighttime sleep, 2.5-4 hours of daytime sleep and 2-4-hour-long wake windows (I included the wider range for each).

What is the problem with this information?

Although I think these books are great, I do not like how they delivered this information for several reasons. By the way, this is true for the third book too, Richard Ferber’s Solve your child’s sleep problems.

First of all, they do not tell you where these numbers come from. Is it data from real children or is it the ideal amount of sleep according to the author? Or is it the recommended amount of sleep based on medical information? They won’t let us know!

Second, they specify very narrow ranges for some of these values; sometimes even just a single number. Who has a baby who sleeps exactly 14 hours a day? No one! I think that this kind of information raises a lot of questions (Is half hour more okay? Is two hours less okay?) and could make many parents feel inadequate.

Third, sometimes numbers don’t add up! This drove me crazy whenever I tried to figure out an age appropriate schedule for my kids. You would think that if you add the minimum number of nighttime sleeping hours and the maximum number of daytime sleeping hours, you would get the total sleep for the day. But, this is not always the case, which can be quite confusing (not the end of the world, but still).

Was Ferber wrong?

Let's look at the third book, Dr. Richard Ferber's Solve your child's sleep problems. He says that at nine months, the total hours of sleep is 12.25 hours, with a typical range of plus/minus one hour and nighttime sleep is 9.5 hours.

If you compare this with the previous two books, you will see that it's considerably less! Nighttime sleep and total sleep is almost two hours less than the recommended amount in the previous two books. Naturally if you calculate the wake window from this, then it comes out as a much higher number: it's almost four hours, which is the higher end of the range in Pantley's book. So who is right?

Let’s look at some real data!

To figure out where the truth lies, I looked at Mark Weissbluth's book titled Healthy sleep habits, happy child. Contrary to the other three books, here, it is clear that the data comes from his own research, the nap survey, that I have mentioned above (1). This makes it more trustworthy, because at least we know that it is based on real children.

According to this research, at nine months, 93% of children nap between 2-4 hours and the mean is 3.1 hours. The extremes can be as little as one hour, or as much as 5.5 hours of daytime sleep! Note, that it doesn’t mean that such extremes are recommended or even healthy – it is just the fact that some children sleep that much or that little.

The values for how much the majority of children sleep during the day align pretty well with all of the previous books' recommendations, but unfortunately, this research was only about naps, so it doesn’t have information about total sleep and nighttime sleep. (Elsewhere in the book, you can find information about total sleep durations that I have copied to the table above, but these values come from other research and I don’t think they can be used together to calculate wake windows.) Plus, this research was done in the 1980s, so it might be the case that children today sleep less or more.

What does recent research say?

Disclaimer: I did not do an extensive literature search. I just looked at the first recent research paper that I came across. This was written by Iglowstein and his colleagues in 2003 (9). They asked parents of 458 children via a questionnaire about their children’s sleep in certain intervals from 1 months to 16 years of age.

The questionnaire method is not the most reliable method, because parents might not remember exactly how much their children sleep. Their memories might be even biased by their own state of sleep deprivation. Asking parents to keep a sleep log might deliver more precise data, but of course it would be more difficult to convince parents to participate in the study. Perhaps, the best method would be to put actigraphs on the children for a few days to measure how much they sleep, but this could be too expensive.

But still, having data about that many children will certainly shed some light on reality! We don’t have any reason to assume that small children are generally sleep deprived (unlike teenagers), so the reality might even inform us about what is recommended or healthy in general.

The mean total sleep duration of 9 months old children was 13.9 hours, the mean nighttime sleep was 11.2 hours and the mean daytime sleep was 2.8 hours. They also give you a wide range where the majority of children fall (the 2nd percentile means that only 2% of children get less sleep than that, and 98th percentile means that 98% of children get less sleep than that).

All values are quite similar to those found in the books, except for Richard Ferber’s book, where total sleep and night time sleep is almost two hours less. This means that Ferber might underestimate the amount of sleep children need!

Take away

So to sum up, a typical kid at nine months of age, naps twice during the day; total naptime is almost 3 hours and total sleep is almost 14 hours. This makes the average wake window to be almost 3.5 hours, but don’t be surprised if in your child’s individual case, these numbers differ with 1 hour plus/minus.

So now you know what experts recommend and what the real data says. Watch out for signs of sleepiness in your child after about three hours being awake and try to figure out a schedule that takes into consideration his unique needs. To help you with that, try this handy schedule calculator.

If you would like to know whether your own child gets enough sleep, click HERE!


  1. Weissbluth, M. (1995). Naps in children: 6 Months-7 years. Sleep, 18(2), 82–87.
  2. Hogg, T., & Blau, M. (2009). Top tips from the baby whisperer: Sleep - Secrets to getting your baby to sleep through the night. Vermilion.
  3. Karp, H. (2015). The Happiest Baby on the Block: The New Way to Calm Crying and Help Your Newborn Baby Sleep Longer (2nd ed.). Bantam.
  4. West, K., & Kenen, J. (2010). Good night, sleep tight: Gentle, proven solutions to help your child go to sleep well and wake up happy. Piatkus.
  5. Dr Sears, W., & Sears, R.N., M. (2005). The baby sleep book. Thorsons. p 58.
  6. Pantley, E. (2020). The no-cry sleep solution (2nd ed.). McGraw-Hill Education. p 43.
  7. Dr Ferber, R. (2013). Solve your child’s sleep problems: The world’s bestselling guide to helping your child sleep through the night. Vermilion. p 10-11.
  8. Weissbluth, M.D., M. (2015). Healthy sleep habits, happy child: A step-by-step program for a good night’s sleep (4th ed.). Ballantine Books. p 425, 445.
  9. Iglowstein, I., Jenni, O. G., Molinari, L., & Largo, R. H. (2003). Sleep duration from infancy to adolescence: reference values and generational trends. Pediatrics, 111(302), 302–307. https://doi.org/10.1542/peds.111.2.302