How much you talk with your child can be really important to their development. In the mid-1990s, an interesting discovery was made about a stark difference in language achievement in children. Researchers Betty Hart and Todd Risley visited families from different socioeconomic groups, spending an hour each month recording them over more than two years.

Going through the data, they found that children from the poorest backgrounds heard one-third as many words per hour as those from higher-income backgrounds. Scaling up, the researchers proposed that by the time the children were four years old, there would be a 30-million word gap between children from poor backgrounds compared to those in wealthier, professional households.

As Melissa Hogenboom pointed out for the BBC, this study was far from ideal. It had a small sample size, and it's not entirely clear if the word gap is as large as the researchers first suggested.

Critics have since shown that low-income children hear many more words than Hart and Risley reported when factoring in language they overhear from conversations both inside and outside the home.

But responding to these critics, another group highlighted that "young children do not profit from overheard speech about topics of interest to adults."

However, if this word gap does exist, it is problematic because language is known to be one of the most important predictors of how well you are going to do later in life, from your earliest school years to university and so, might even be an indicator of the success of your future career.

Whether we're learning basic numeracy or articulating memories, we need language.

Scientists are even able to show how the brain responds to early language exposure. One group, led by Rachel Romeo, a neuroscientist and speech language pathologist at Boston Children’s Hospital, showed that conversational interactions can have a visible benefit on brain development.

The team recorded conversations in families’ homes monitoring both the amount of language they were exposed to and the number of conversational turns and discovered that children who had more turn-taking conversations were better at language comprehension tasks.

Indeed, we have evidence that it is not passive hearing – or even the amount of words a child is exposed to – that matters most. Instead, it is the quality of the conversation that is important. The back and forth turn-taking nature that requires listening and responding.

It’s what Hirsh-Pasek and her long-time collaborator Roberta Golinkoff refer to as a “conversational duet”, as “you can’t sing it alone”. In fact, another study found that if a conversation is interrupted by a phone call, the child does not learn a newly presented word (they will learn it if the conversation is not interrupted).

Even if Hart and Risley's study wasn’t perfect, the idea that a significant socioeconomic gap exists has been replicated by numerous studies.

In 2008, for instance, Meredith Rowe of Harvard University found that types of conversations do differ significantly between low- and high-income families – in part due to the differing levels of education reached by the parents in these groups.

Though a word gap can have lasting consequences, the good news is that all parents talk to their children at least sometimes. And if parents would focus more on the quality of interactions rather than quantity, then children could benefit.

The more social experiences they have, whether with their parents or with any other caregivers around them, the more they will learn.

While the stress of day-to-day life can leave less time for talk and play, with a few subtle tweaks in how we speak to children – and how we listen to them – we can literally grow their brains for the better.