Most children born with congenital hypothyroidism and correctly treated with thyroxine grow and develop normally in all respects. Even most of those with  undetectable T4 levels at birth develop with normal intelligence, although as a population academic performance tends to be below that of siblings and mild learning problems occur in some.

Some studies, however have found a slight reduction in verbal, math and IQ scores as well as slight deficits in memory and attention in some children restored to normal thyroid levels more slowly, due to delayed diagnosis .