Righty or Lefty? When Will You Know?

Righty or Lefty? (image)

Wendy Hunter, MDWendy Hunter, MD
Pediatrician | Mom | Founder of BabyScience.info
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Will your child be an accomplished athlete or mathematical genius? We grownups love looking for subtle clues to our child’s future self. Surely you’ve seen your baby reach with his left hand and wondered – could your genius-athlete be a lefty?

A preference for one hand can be determined around 6 months. So if you suspect your baby is right-handed, you’re probably correct. However, children’s hand use fluctuates until kindergarten. For example, a completely normal child shifts between picking up objects with only their preferred hand, then a few weeks later using both hands equally. And they often shift from using mostly their right to using mostly their left hand several times before 18 months.

We have a stronger eye and ear; babies even have a preferred side for their leg kicks and head turns. Even unborn babies have a preferred side. In a study of 75 fetuses observed in utero and re-examined at age 12, all 60 right hand suckers were right-handed and 10 of the 15 left hand suckers were left-handed. So hand preference starts earlier than we thought!

There is good reason for this. Our brains are wired to make us ambidextrous during times when we are learning new motor skills. For example, kids who predominantly use their right hand will start using both hands equally when they are learning to crawl. In one study, researchers observed a group of kids in a task of taking a toy out of a box at the time when they were just learning to crawl . Right-handed kiddos used their left as often as their right hand during multiple trials of the task. Just as they were alternating their hands while crawling, they were alternating use of their hands while playing. When these same kiddos started taking their first steps they suddenly began using both arms together to open the box and take out a toy. They used their arms symmetrically for tasks during the time that they were precarious walkers. While walking they held their arms in a high guard position to control their balance. As soon as they became stable walkers, they began to lower their arms along the side of their body while walking and returned to one-handed reaching in the task.

Hands look symmetric, yet we choose a favorite. And they look the same, but don’t work quite the same.

While a young child will often have a preferred hand, there’s a difference between hand preference and true adult-like handedness – as in the dominant use of one hand, and relative clumsiness with the opposite hand. There’s no consensus about when complete handedness is attained: researchers put it anywhere between ages 3-12. Most studies have shown that a child’s preferred side is set by age 4. Children need time and practice to develop the performance difference that we see between the two hands in adults. Practice using one hand more than the other helps us become coordinated at precise tasks like sewing and holding a pen. So there is a period of several years when kids refine their fine motor skills and they may occasionally use their non-dominant hand, particularly when they are learning new skills including cutting with scissors and drawing.

90% of the population is right-handed.

When babies pick a favorite hand there is definitely a genetic influence, however there are subtle things adults do to encourage the preference for one hand. Children copy or mirror the adults in their lives; so if you eat with your left hand, they may give it a try too. And if you consistently carry your child on your left hip with their left hand free, they may preferentially develop that side.

Whether a child is right or left-handed depends on their environment (e.g. the variety of toys and activities they are exposed to) and their genetics. While you can’t control genetics, you can provide a range of both simple and complex activities involving a variety of objects to develop both of your child’s hands. Do a great job and, who knows, maybe you’ll raise an ambidextrous genius-athlete.

This post was originally posted on BabyScience.info on 4/15/2016.

Wendy Hunter, MDAbout Wendy Hunter, MD

Dr. Wendy Hunter, MD is an Assistant Clinical Professor of Pediatrics at UC San Diego and practices pediatrics in the emergency department at Rady Children’s Hospital. She blogs at BabyScience on the science behind scary (but normal) baby symptoms and quirky kid behaviors. You can also find Dr. Hunter on Twitter and Facebook.



17 Comments on “Righty or Lefty? When Will You Know?”

  1. Very interesting article, we have both left and right handed in our family. curious to see what my new grandson will be.

  2. Very interesting! I will watch my little granddaughter to see if she is using her left hand or right hand more.

  3. wow this is really intereting i have a one year old and i will be watching for now one to see what he use thanks for this great article

  4. Who knew hand preference started so early – very interesting! I particularly found it interesting that a a child’s preferred side is set by age 4.

  5. Wow what an amazing read, my twins are only 4 months old but already started with the hand sucking.. I never knew there was clues to weather they could be left or right handed and I certainly didn’t know you can’t really tell for sure at such a young age, lovely article, thanks for the insite

    1. Glad you liked it, Tanya! We always learn so much from Dr. Hunter’s columns! We hardly knew any of that either! Thanks for the comment.

  6. Very interesting article.. I’m left handed and none of my 3 children are.. I thought that was k8nd of strange..

  7. My youngest son is ambidextrous – colors with his right hand and writes with his left hand. I never tried to switch him, he does well just the way he is.

  8. Very interesting article. I knew that babies learn early but never realized or thought about carrying a baby on your help would lead to which hand they would use.

    1. That info was new to us too, Debbie! Dr. Hunter’s articles are always fascinating! Thanks for the comment.

  9. I keep telling my husband that my son needs to be left handed like his grandma. Also so he can be a left handed pitcher.

    1. :) Sounds like you’re trying to raise a good little baseball player, Sarah! LOL!

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