Handedness is the consistent preference for using one hand over the other for skilled tasks. This developmental milestone determines if a child is right-handed, left-handed, or uses a combination of both. Establishing this side preference is a gradual process, making it difficult to pinpoint when a child’s choice is finalized.
Developmental Stages of Hand Preference
Infant movements are typically non-lateralized, meaning both hands are used equally for reaching and grasping during the first year of life. Babies often switch hands, using whichever hand is closest to a desired object. A strong, consistent preference for one hand before 18 months is usually temporary and does not reliably predict later handedness. An unusually early and strong preference in infancy can sometimes signal a mild neurological issue, such as weakness on the opposite side, and warrants professional observation.
Between 18 months and three years, the first hints of preference emerge during fine motor tasks. A child might start consistently using one hand for drawing or self-feeding, though they still switch hands frequently. During this period, the brain tests and refines the hand that will eventually become dominant for single-handed activities.
Handedness generally becomes consistent between the ages of three and five years. By the time a child enters kindergarten, around age five or six, most will have established a dominant hand for precise tasks like writing and cutting. The dominant hand takes the lead for skilled activities, while the non-preferred hand assumes a supporting role, such as holding the paper steady.
The Biological Drivers of Handedness
Hand preference is closely tied to brain lateralization, the specialization of function between the brain’s two hemispheres. Motor control is contralateral: the left hemisphere controls the right side of the body, and the right hemisphere controls the left side. Approximately 90% of the population is right-handed, associated with the left hemisphere being dominant for fine motor control and language.
Handedness is a polygenic trait, influenced by the interaction of many genes rather than a single one. Twin studies suggest genetic factors account for about 25% of the variance, indicating a substantial role for non-genetic influences. These genetic influences likely affect the structural asymmetries of the brain, establishing a left-right axis early in development.
Prenatal factors also contribute to this preference, with studies showing fetal hand preference for thumb-sucking as early as ten weeks gestation. This early preference suggests that the biological foundation for left or right specialization is laid long before a child grasps toys. The combination of genetic predisposition and early environmental factors shapes the eventual consistent hand choice.
Navigating Mixed Preference and Late Development
Some children exhibit mixed handedness, preferring different hands for different tasks, such as writing with the left hand but throwing a ball with the right. This differs from true ambidexterity, which is the ability to perform all tasks with equal skill using either hand. True ambidexterity is extremely rare, occurring in less than 1% of the population.
For some children, a dominant hand may take longer to emerge, sometimes not becoming consistent until age five or six. This delayed settling is not a cause for concern unless it is part of a broader pattern of developmental delays. The brain is simply taking a longer path to establishing efficient motor patterns.
A sudden change in established handedness or a strong preference for only one hand before 18 months can be clinically significant. A sudden shift may signal a problem with the previously non-preferred hand or arm. Any unexpected change in a child’s hand use should be discussed with a healthcare professional to rule out underlying issues.
Should Parents Influence Hand Choice?
Handedness is a biologically determined trait, and expert consensus advises against forcing a child to use a specific hand. Intervening to change a child’s preference, such as forcing a left-handed child to use their right hand, can lead to frustration and interfere with motor skill development. This intervention does not alter the underlying brain organization that dictates the preference.
The most supportive approach is to provide an environment that allows the child’s natural preference to emerge. Parents can encourage the use of both hands by placing objects and toys directly in the child’s midline, ensuring neither hand has an initial advantage. This strategy allows the child to naturally select the hand that feels most comfortable and efficient for the task. The goal is to promote comfort and competence in the hand selected for skilled activities.