Although it’s difficult to say what “normal” intelligence is, many experts in the field of development can define the sequence and rate of mental development in the average child and use this to predict intelligence. Remember that the average child doesn’t exist: an average is theoretical, so you should never apply it to your own child, nor should you compare him with other children of his age.
There are major variations in the rate of development from child to child, and there is no correct age when any milestones should be reached. Most children experience growth spurts and pauses. Some show a temporary developmental pause and then go on to develop normally; others appear advanced in infancy but turn out to be average in later years. Then there is the well- known “slow starter,” the child who is slightly behind in infancy, yet later does very well. A very few children show a progressive slowing in the rate of development. There are children in whom it is so difficult to predict the course of development that the outlook can only be guest at cautiously and after repeated examinations. The conclusion is that you should not attempt to predict your baby’s level of intelligence.
The great majority of babies turn out to be perfectly normal children. Sadly, a very small number lag seriously behind in all areas of development, with both physical (motor) and mental development being markedly delayed. Throughout the first three years, the developmentally delayed child shows below- average concentration and interest in his surroundings. He is late in aspects of development such as head control, sitting up, and grasping his toes, and in outgrowing his primitive birth reflexes, which may persist long after the usual age.
While there are clear indicators that a child is developmentally delayed, it is more difficult to spot the child with above- average abilities. A particularly intelligent baby may reach developmental milestones earlier than average, but the real indicators of his superior intelligence are more subtle: he’ll display a greater variety of behavior, a greater interest in his surroundings, and more interaction with his environment than the average baby.