Why do some children do better at school than others?

Some children have an easier time in learning than others. That’s not to say that some children cannot learn — they just need more time or more guidance. A straightforward result of children’s differences in the ability to learn are their differences in school grades. Some children come top of their class and quickly master the curriculum, while others need extra tutoring and have to practice harder and then they may still get lower grades.

Of course, school grades aren’t everything and children can be smart in many different ways that are not limited to the school environment. For example, some children are amazing athletes, others are fantastic singers, and again others are brilliant at leading the group of neighborhood kids. However, school grades are very important: In the UK, like in most other countries, school grades regulate the access to further education. For example in Britain, teenagers’ GCSE grades will influence their decision to go on to A-levels next, which in turn will affect if and which university they will apply to.

The 30 million word gap

In the 1990s, Betty Hart and Todd Risley published a seminal book on their efforts to understand the origin of children’s differences in language development. Both researchers had taught children in kindergarten and primary school settings, and they had come to realize that they differed substantially in verbal ability. Hart and Risley recognized that these differences in verbal ability were evident already before children had started kindergarten or school, and they suspected that these differences in verbal ability were related to the different family backgrounds that children experienced. In particular, they hypothesized that children from families that spoke only little at home would show worse verbal ability than children from chattier families.

To test this idea, Hart and Risley started a longitudinal study that followed 42 families with infant children over the course of two and a half years. Each month, research assistants visited the families and observed them for one hour. To do so, the research assistant would follow the family child with a microphone and tape recorder in hand, trying to document everything the child heard and said over the course of an hour. Back at the lab, the research assistant then transcribed the recording and prepared the data for analysis.

Later Hart and Risley extrapolated the data from the hour-long recordings to match 24-hour days and thus, estimated how many words each child heard and spoke per day. The made two key discoveries.

First, children’s language experiences at home differed primarily in quantity. That is, children heard pretty much the same types and kinds of words across all families but in some, they heard these words much more often. Quite dramatically, Hart and Risley found that some children hear 30 million fewer words than others by the time they are 4 years old.

The second finding revealed that children who heard more language at home also showed better verbal ability themselves, which in turn was linked to better general cognitive ability and school performance. In other words, children from families that spoke more with one another developed greater language skills. These better language skills then helped getting better grades in school and developing overall greater thinking skills.

Overall, Hart and Risley’s work suggest one answer to the question: Why are some children smarter than others? The smart ones hear more words at home as they grow up.


At the Hungry Mind Lab, we sought to replicate and extend Hart and Risley’s work. Specifically, we wanted to test a larger sample, from Britain, and observe them unobtrusively — without a research assistant following the children with a tape recorder in hand — for a longer period than merely an hour at a time. We wanted to achieve a well-powered study that accurately captured children’s early life language experiences.

With funding support from the Wellcome Trust, we recruited overall around 120 families from South East London, who had young children aged 24 to 48 months. Each family completed an extensive background survey online, before they had a box with the study materials hand-delivered to them.

The box included LENA (Language Environment Analysis) digital language recorders, about the size of a floppy disk, that children wore inserted in designated chest pockets in their t-shirts. Parents also received a testing booklet to complete together with their child to assess the child’s cognitive development.

Parents completed 3 full days of digital recordings with their children, as well as the cognitive testing booklet over the course of the next month. On recording days, the digital language recorders documented everything that the child heard or said in a six-foot radius. Once the recordings were done, a research assistant visited the families again to pick up the study box with its materials.

Revisiting the 30 million word gap

We finished collecting all data in March 2017 and since, we have been working to prepare the data for analysis. While this is work in progress, we have two preliminary results.

First and like Hart and Risley suggested, we found that families differed vastly in the language environment that they provided for their children. On average, children heard about 18,000 words per day but the range was enormous. In one family, the child heard 3,200 on a day, while in another the child heard 45,500 words. That’s a 14-fold difference!

Our second finding is about the stability of these differences in language. Hart and Risley observed, like us, that there were vast differences between families in how many words children heard. However, Hart and Risley did not study to what extent families differed within themselves across time in how much they spoke. That is, we don’t know if a child hears the same or at least a similar number of words day after day in their family, or if a family speaks a lot on one, and much less on another day.

It makes a lot of sense to assume that families don’t always speak the same amount to one another over the course of a day. They are likely to chat more over meals, like lunch and dinner, and less during nap and play time, when children are by themselves. But across entire days, we’d expect that chattier families always speak more than quieter families.

In our sample, we found that 47% of the variance in the number of words that children heard across three days occurred within families. That means that about half of the differences in the amount of words that children hear per day come from their own family. Or expressed differently, families change how much they talk to one another day after day.

This finding challenges the notion of a 30 million word gap, at least one that is tied to a fixed number. Rather it seems that children’s early life language experiences fluctuate a lot for each child. We have yet to work out what that means for understanding the role of environmental influences for children’s verbal and cognitive development.


For more information on LENA and how it works, please visit the LENA manufacturer’s website.  You can also find more questions and answers about LENA, as well as parents’ experience reports of using LENA.

Do you have a different question?2017-05-26T12:53:20+00:00

If you have a different question or would like to get in touch with the LENA team, please email us at lena@hungrymindlab.com.

What will you do with the data?2017-05-26T12:50:16+00:00

We are mainly interested in three parameters about language that LENA derives automatically by analysing the recordings with specific software package. The three parameters are (a) the number of words the child has spoken, (b) the number of words the child has heard, and (c) the number of conversations that the child has had, where the child says something, another person responds, and the child says something back again. We want to see how these three parameters relate to children’s general cognitive development and to their parents’ language and reading habits.

This is in many ways an exploratory study: we try to find out if parents and children enjoy using LENA, and if the parameters extracted by LENA software are useful for studying childhood development. In case we find something interesting, we will try to publish our findings in scientific journal. In that case, we’ll also probably try to start an even bigger project with more children and families to collect even more data on language development. No child or family will be identifiable from the data, and all recordings will be stored safely and anonymously.

Is the device easy to use?2017-05-26T12:48:45+00:00

The LENA device is very easy to use: it has two buttons, one for power and one for turning the recording on and off. Slip the LENA device into your child’s vest after pressing the record button and at the end of the day take the LENA device out of the vest and press the power-off button. That’s it.

Do parents feel self-conscious on recording days?2017-05-26T12:49:09+00:00

Most parents forget about the LENA device in their children’s vest within the first 20 minutes of the recording and go about their normal routine. It is possible to turn off the recording for some time, even though we typically advise not to turn them off, because it is easy to forget to turn it back on.
The recordings will be analyzed by the LENA software package, which provides counts of the number of words that children and adults have spoken on the recording. We will also transcribe and analyse two 5-minute segments from each day’s recordings. These segments will be selected from times when the child spoke a lot, so that we can look in more detail about how children develop their language. The recordings will be stored without identifiers to protect participants’ anonymity.

Do children notice the recording?2017-05-26T12:45:32+00:00

In almost all cases, the answer is a straightforward no. LENA devices are inserted to clothing that is specifically designed for LENA use and worn by the children. We have a wide selection of t-shirts, tops and vests in various colours and patterns. All of them have a small pocket in the front. Parents are advised to insert the LENA device in the pocket in child’s vest or t-shirt when the child is not looking. This way, the child doesn’t get curious about the device and trypically doesn’t even notice it.

The recording device weighs about 2 ounces (60 grams). The clothes are designed to fit children comfortably and to be optically liked by parents and children. Wearing one of these clothing items and the LENA device does not restrict children in any way in their movements or daily routines. The LENA devices are completely safe to use, and an increasing number of families, mainly in the United States, apply it already to track the children’s language development at home.

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