John Troulis, age 12, of North Brunswick, N.J., for his question:

WHAT MAKES A PERSON LEFT HANDED?

When a child is about 18 months old, he goes through a period of bilaterality when he shows no preference for either the left or right hand. This is followed at about the age of 2 with a definite preference for a dominant hand.

Most people are right handed. However, about 6.5 percent of adult males are left handed and so are 4 percent of the female adults. The incidence is higher in children and decreases gradually as adulthood is reached.

What makes a person left handed? No one is sure, exactly. It is found more often among twins than in the general population, with only one twin being left handed.

A child should be allowed to develop his own natural handedness, be it left or right.