Cribsheet: A Data-Driven Guide to Better, More Relaxed Parenting, from Birth to Preschool (The ParentData Book 2)

by Emily Oster

What are these normal ranges? For that, we can go to the data. The World Health Organization, using data from six countries, calculated the range of the 1st percentile to 99th percentile for each of a variety of outcomes among healthy children. The children they studied do not have diagnosed motor issues, so their argument is that this can be seen as the range of normal development.6 Milestone Range Sitting without support 3.8 months to 9.2 months Standing with assistance 4.8 months to 11.4 months Crawling (5% of kids never do) 5.2 months to 13.5 months Walking with help 5.9 months to 13.7 months Standing alone 6.9 months to 16.9 months Walking alone 8.2 months to 17.6 months

Kids younger than school age get an average of six to eight colds a year, most of them between September and April.7 This works out to about one a month. These colds last on average fourteen days.8 A month is thirty days. So in the winter, on average, your kid will have a cold 50 percent of the time. On top of this, most kids end their cold with a cough that can last additional weeks. It adds up.

Most colds are minor, although they increase the risk of ear infection and other prolonged bacterial infections (bronchitis, walking pneumonia), which is why most doctors will tell you to come in if you are concerned, or if a fever lasts longer than a couple of days, or if your child gets worse after they’ve seemed to get better. Of these complications, ear infections are the most common. About a quarter of kids will have an ear infection by the age of one, and 60 percent by the age of four.9 If

In the case of Sesame Street, there is actually good research suggesting that exposure to the show increases school readiness in kids ages three to five.

In all three age groups, when kids watched an actual person doing the action, some of them were able to replicate it a day later. The video demonstration was much less successful—the twelve-month-olds learned nothing, and the older kids learned much less than from seeing a live person do it. Another example is a study where researchers tried to use a DVD recording to maintain exposure to non-native sounds. At birth, children are able to learn the sounds from any language, but as they age, they specialize in the sounds they hear regularly. Researchers tried to maintain exposure of English-speaking nine- to twelve-month-olds to Mandarin-language sounds, either through a live person or through a DVD.2 The live person worked well, the DVD did not.3

The study’s authors noted that the most significant predictor of both how many words the children spoke and how fast their vocabularies grew was whether their parents read them books. Other authors have extended versions of this study to kids up to age two and found similar results.

Videos may be a dud for baby learning. But there is more evidence that older kids can learn from television.

Kids learn songs from movies and from shows, and can pick up names of characters and basic plot elements. Researchers in the lab have shown that three- to five-year-old kids are able to learn words from television.

Early on, researchers used randomized trials to evaluate the effects of Sesame Street. In one evaluation, the group of families assigned to the treatment group had their televisions hooked up so they could access the show more effectively.7 The researchers found, over a period of two years, improvements in various measures of school readiness, including vocabulary. The effects of Sesame Street seem to be long-lived. A more recent study looked back at the early years of the show and compared the kids who got early access to it—because of better TV reception—to those who got later access. The earlier-access kids were less likely to be held back in school at older ages.8 The show had bigger positive effects for children from more disadvantaged backgrounds, which could be due to differences in the other activities in their day, or to something else.

Their results suggest that watching more TV under the age of three lowers test scores; not a huge amount, but by the equivalent of a couple of IQ points.

However, watching TV at older ages doesn’t seem to matter. When the authors compared, say, the kids who watched only a little TV before age three and then a lot between ages three and five to the children who watched little TV before age three and little later, they found their test scores to be no different. If anything, the kids who watched more TV later had higher test scores than those who watched less.

The idea was to see how having TV access as a young child related to test scores when kids were in school at slightly older ages. Jesse and Matt found no evidence that more exposure to television at an early age negatively affected later test scores.

Children under two years old cannot learn much from TV. Children ages three to five can learn from TV, including vocabulary and so on from programs like Sesame Street. The best evidence suggests that TV watching in particular, even exposure at very young ages, does not affect test scores.

Take, for example, age 24 months. This data says that the average child—that’s the 50th percentile line—at 24 months has about 300 words. A child at the 10th percentile—so, near the bottom of the distribution—has only about 75 words. On the other end, a child at the 90th percentile has close to 550 words. For younger children, these surveys and data focus on

One main takeaway from these graphs is the explosion of language after fourteen or sixteen months. Even the most advanced one-year-old has only a few words. At eight months, virtually no children have any words or gestures.

It is worth noting here that kids who are bilingual—that is, their parents or caregivers speak to them in two different languages—tend to be slower to talk, although when they do, they can speak both languages.

The timing of language development does have some link with later outcomes—test scores, reading—but the predictive power is weak for any individual child.

and the findings from this data—is supported by the literature. Studies from the 1960s and ’80s show an average age of twenty-five to twenty-nine months for daytime toilet-training completion, and virtually all the children were trained (for the daytime) by thirty-six months. In contrast, in more recent cohorts only 40 to 60 percent of children have trained by thirty-six months.

They found three factors significantly associated with later training. The first—and probably the one that explains variation over time—is later initiation of potty training. Children who start training later complete training later. The other two factors relate to poop. Children who were frequently constipated, or who showed resistance to pooping in the potty (formally “stool toileting refusal”—more on this to follow) tended to train later. The authors argued that these factors could also increase over time, although they largely put the blame for later training on the later initiation of the process. It is interesting to speculate why people have started training later in recent years. My mother insists it relates to diaper quality—diapers used to leak a lot, which made it much less fun to use them.

The authors suggest that if what you care about is when potty training is done, there is not much point to starting before twenty-seven months or so. But it is the case that after this, starting earlier does generally mean finishing earlier. If you start training at twenty-seven or twenty-eight months, you can expect to be done by around age three, but it will take ten months to do it. If you start at age three, you finish later, but it’ll likely take you less than six months to fully train.

The bottom line is that potty training is really all about what works for your family and your kid. The evidence on changes over time suggests it is possible to train your child at a younger age than is now typical, if you want to. To do this, you’ll probably have to adopt a more goal-oriented approach (rather than a child-led approach). Or you can wait until your child decides they are ready, which will probably be when they are closer to three years old or even a bit older.

There is no evidence linking age of potty training with any later outcomes like IQ or education.10 So if your child is trained early, that might be great (for you) but irrelevant in the long term.

One study of four hundred children, published in 2003, showed that the length of refusal (i.e., the number of months this goes on) decreased with a child-oriented intervention where, among other things, parents made a big deal about the child pooping in the diaper before potty training started.13 This means saying things like, “Wow! You pooped! That’s so great!” and so on. The kids in this treatment were no less likely to have the problem at all, but it lasted for less time.

In contrast to the day, staying dry at night basically requires that your body wakes you up if and when you need to pee. This ability develops at different ages in different children. By the age of five, 80 to 85 percent of children are dry at night (meaning not that they do not pee, but that if they do, they wake to use the bathroom).

Elimination communication, however, is a method in which parents train—perhaps from birth—to recognize the signs that their child is going to pee or poop and then quickly put them on the potty. Obviously with a baby that cannot sit up yet, you cannot put them on a toilet—the idea here is to hold them in your lap over a bowl or similar so they get the association. There are very few studies about elimination communication. One early report surveyed parents engaging this strategy and showed that, indeed, many parents reported their child did give signs of needing to use the toilet, even at a very young age.16 The children in the study were trained very early—by seventeen months, on average—with no adverse effects.

Broadly, all these emphasize a few key elements. First, recognize that children are not adults, and you usually cannot improve their behavior with a discussion. If your four-year-old is taking their shirt off in the museum, they will not respond to a reasoned discussion about how you actually do need to wear a shirt in public places. The flip side of this—more important—is that you shouldn’t expect them to respond to adult reasoning. And as a result, you should not get angry the way you would if, say, your spouse was stripping in the museum and didn’t stop after you explained why they shouldn’t. All these interventions emphasize not getting angry. Don’t yell, don’t escalate, and definitely don’t hit. Controlling parental anger is the first central part of the intervention.

Breathe. Take a second. I once told my children, “I’m so mad right now, I’m going to the bathroom for a while to calm down.” (It’s the only door in the house that locks.) And I did, only coming out when I thought I could handle not only them, but myself.

An extension of this your-child-is-not-an-adult observation is that it is probably not a good use of your time to think a lot about why your small child is having a tantrum. There is a strong temptation to try to figure out what exactly is the issue—to try to get them to articulate the precise problems they are having. Even if they can talk, this is likely to be fruitless, since they probably do not know. Tantrums happen for all kinds of reasons. Working on disciplining the tantrum behavior is the goal.

Second, these approaches all emphasize setting up a clear system of rewards and punishments and following through on them every time. For example, 1-2-3 Magic develops a system of counting (to three, obviously) in the face of disruptive behavior, and if three is reached, there is a defined consequence (a time-out, loss of a privilege, etc.). Finally, there is a strong emphasis on consistency. Whatever the system you use, use it every time. If the consequence of counting to three is a time-out, then there needs to be a time-out every time, including, say, in the grocery store. (The book suggests you find a corner of the store, or bring a “time-out mat” with you.)

As an extension, if you say no to something, you stick to no. If your kid asks for dessert and you say no, you cannot then later say yes if they whine for long enough. This basically makes sense—what do they learn from that? That whining will sometimes work.

Smaller trials of 1-2-3 Magic with longer follow-ups have shown similar impacts, with authors arguing that the effects of these programs can be seen even two years later.2

One of the main tenets of these parenting approaches is that discipline should be reserved for actual bad behavior, not for things that are merely annoying. At least one of the books I read on this suggested earplugs. It is worth noting that for an older kid, if they know you are annoyed, they’ll probably do whatever annoying thing they’re doing more.

The authors argued that spanking does have negative long-term impacts, especially on behavior problems. Spanking at age one increased behavior problems at three, and spanking at three increased behavior problems at five. These results held even with controls for earlier behavior—spanking at three relates to behavior problems at five, even controlling for behavior problems at three.

What’s Going On in There?, for example, is a great primer on how the baby and toddler brain develops. Here I’m going to focus on a limited set of questions.

The results show large positive impacts of reading on children’s achievement. Children who are read to more as young children achieve greater reading success in school. One concern is that these kids just generally get more attention; this is a possibility, but the effects do not extend to math, so the authors argued that it does seem to be something about reading in particular.

What the researchers found was that children who were read to more at home showed more brain activation in the areas of the brain thought to be responsible for narrative processing and imagery. Basically, it looked like kids who were read to more were processing the story more effectively.

In particular, researchers have found that the benefits are bigger with more interactive reading.6 Rather than just reading a book, kids benefit from being asked open-ended questions: “Where do you think the bird’s mother is?” “Do you think it hurts Pop when the kids hop on him?” “How do you think the Cat in the Hat is feeling now?”

Putting this together, it again probably depends on the other options for your child during the day, but I’d say the weight of the evidence is that some preschool environment around age two or three will, on average, improve the ease with which they transition to school.

A related question is whether you should favor one preschool “philosophy” over others. The three philosophies you will most commonly encounter in your preschool exploration are Montessori, Reggio Emilia, and Waldorf. Montessori education focuses on a particular classroom structure and a set of materials. There is an emphasis—even in young children—on the development of fine motor skills. These schools generally refer to children’s play as “works.” Young children are typically exposed to letters and numbers and writing them in sand, counting blocks, and so on. Reggio Emilia–inspired schools put more emphasis on play, with typically little formal letter or number exposure at preschool ages. (One Reggio Emilia–style preschool I visited told me they explicitly do not spend any time on letters for the three- and four-year-old class, and wouldn’t even display letter cards around the room. This seemed a little extreme.) The Waldorf schools have a heavy outdoor component and, similar to Reggio Emilia, are largely play-based. The Waldorf principles focus on learning through play and art, and tend to also have some domestic-activity component (cooking, baking, gardening).

There is some support for the value of reading to your children starting in infancy. Your baby cannot learn to read. Whether your two- or three-year-old can is unclear, but it would be very unusual for them to be a fluent reader. Evidence on the value of different preschool philosophies is limited.

We can see this in a variety of studies that look at the relationship between parenthood and marital satisfaction. These go back as early as 1970, with a paper showing that between the pre-childbearing period and the period of having school-aged children, the share of mothers reporting low marital satisfaction rises gradually from 12 percent to 30 percent, with an abrupt jump in the first year of the child’s life. The marriage does not recover until parents become grandparents.3 Meta-analyses of more recent data show similar things—parents are less happy with their marriages than nonparents. The changes seem to be most abrupt in the first year, and then there is some recovery, although not complete.4 As one study helpfully notes, “In sum, parenthood hastens marital decline. . . .”5 It is worth noting that these studies do tend to find that people who are happier before they have kids recover better, and that planned pregnancies are less impactful than unplanned ones. And the effects are not enormously large. Many people are still, on net, happy with their spouse. Just, you know, slightly less.

The second thing to say is that, as is a common refrain in this book, sleep is a key issue.15 Drops in marital satisfaction are higher in couples with kids who sleep less. Lack of parental sleep contributes to depression (in both parents) and correspondingly to less-happy marriages. You need sleep to function, and sleep deprivation affects your mood. If you are cranky, you’re cranky with your partner. If they are also tired, they are also cranky. Cranky, cranky, sad, angry.

Some small-scale randomized interventions do show some effectiveness. One is the “marriage checkup.”16 The idea behind this is to have an annual meeting—possibly facilitated by some professional—to actually discuss your marriage. What do you feel is working? What isn’t working? Are there particular areas of concern or unhappiness? These checkups seem to result in improvements in intimacy (i.e., sex) and marital satisfaction. This makes sense in the abstract; it’s helpful to talk things through methodically with a neutral third party. Beyond this particular intervention, there is other evidence in favor of therapy more generally—group couples therapy, counseling programs beginning before birth and continuing after—to improve relationships.17 Speaking in broad generalizations, these focus on communication and positive solutions to conflict.

The results from the best of these papers generally show that the number of children plays a relatively little role in determining schooling or IQ.2 They do find that birth order matters. Later-born children tend to do (slightly) worse on IQ tests and get less schooling than their earlier-born siblings. This may be due to parents having less time and resources to devote to them. But it’s not the number of children that drives the association. A firstborn child with two siblings seems to do the same as a firstborn child with one.

found some evidence of more “academic motivation” among only children, but no differences in personality traits like extroversion.4 Even this fact about academic motivation may be more about birth order—firstborn children score higher on this regardless of whether they have siblings—than about being an only child.

So let’s say you decide you want to have another kid. Does the data tell you when you should do it? Again, no, not really. To the extent research has been done on “optimal birth spacing,” it tends to focus on two things: the relationship between birth spacing and infant health, and the relationship between birth spacing and long-term outcomes like school performance and IQ.