Lying is wrong. Everybody lies.

So when do the 98 percent who think lying is wrong become the 98 percent who lie?

It starts very young. Indeed, bright kids—those who do better on other academic indicators—are able to start lying at 2 or 3. “Lying is related to intelligence,” explains Dr. Victoria Talwar, an assistant professor at Montreal’s McGill University and a leading expert on children’s lying behavior.

Although we think of truthfulness as a young child’s paramount virtue, it turns out that lying is the more advanced skill. A child who is going to lie must recognize the truth, intellectually conceive of an alternate reality, and be able to convincingly sell that new reality to someone else. Therefore, lying demands both advanced cognitive development and social skills that honesty simply doesn’t require. “It’s a developmental milestone,” Talwar has concluded.

This puts parents in the position of being either damned or blessed, depending on how they choose to look at it. If your 4-year-old is a good liar, it’s a strong sign she’s got brains. And it’s the smart, savvy kid who’s most at risk of becoming a habitual liar.

By their 4th birthday, almost all kids will start experimenting with lying in order to avoid punishment. Because of that, they lie indiscriminately—whenever punishment seems to be a possibility. A 3-year-old will say, “I didn’t hit my sister,” even if a parent witnessed the child’s hitting her sibling.

Most parents hear their child lie and assume he’s too young to understand what lies are or that lying’s wrong. They presume their child will stop when he gets older and learns those distinctions. Talwar has found the opposite to be true—kids who grasp early the nuances between lies and truth use this knowledge to their advantage, making them more prone to lie when given the chance.

Many parenting Websites and books advise parents to just let lies go—they’ll grow out of it. The truth, according to Talwar, is that kids grow into it. In studies where children are observed in their natural environment, a 4-year-old will lie once every two hours, while a 6-year-old will lie about once every hour and a half. Few kids are exceptions.

Read it all in New York Magazine.