If you’re a parent, you’re familiar with the scenario: Your tuck your child into bed. Your child demands you read Where the Wild Things Are to them. You read it to them the previous evening. And the evening before that. And the evening before that. Where the Wild Things Are is seared into your brain. Its words no longer carry any meaning. You can recite them without actually looking at the book. Chillingly, they may even ask you to read it again—that very same night.

There’s a good reason kids like hearing the same bedtime story over and over again, and it has nothing to do with trying to drive their parents crazy. (They save that for dating, driving, and political discussions in their teenage years.) Kids enjoy the familiar, and with bedtime, it’s a ritual of a warm bed, a loving parent, and another constant: their favorite story. A bed offers comfort and warmth, ideal conditions for learning. During the day, either at home or school, kids can experience heightened levels of the stress hormone cortisol in response to new and potentially frightening situations. By being in a safe place—like their bed—and hearing a familiar story, their cortisol levels will decrease.

And whether kids understand it or not, repetition is offering tremendous benefits for their intelligence. Speaking with Parents.com, Virginia Walter, Ph.D., an associate professor of education and information studies at the University of California, Los Angeles, said that kids that begin to know a story by heart can develop their logic skills. They’re rehearsing their ability to predict events based on existing knowledge.

For example, when a parent reads the classic The Monster at the End of This Book, a child who has heard the story once will anticipate that the narrator, Grover, is the titular monster. They’ve “predicted” an outcome. Pretty soon, they’ll use their awareness of patterns to make assertions about other things, like science and math.

Repetition has also been shown to increase children's vocabulary. By not having to concentrate on the narrative twists and turns, kids can focus on identifying and learning new words. In one small study conducted in England, two groups of 3-year-olds were read stories that had made-up words like sprock or coodle in four different parts of the story. One group heard the same story three times. Another group heard three different stories, all with the same made-up words. That means each child heard the words 12 times total. Although the frequency was the same, kids hearing the same story throughout the week were able to remember the words both immediately and after a delay of a few days or more. The group hearing different stories had problems with retention—they couldn’t remember a word learned the week prior.

Eventually, you will want to set a favorite book aside. If a child’s vocabulary is built on one book, it’s going to be rather limited. But parents should take some solace in the fact that all of that ponderous repetition is doing someone in the room a lot of good.