All this is due to one fact, and one alone: _the school tends to promote children by age rather than ability_. The bright children are held back, while the dull children are promoted beyond their mental ability. The retardation problem is exactly the reverse of what we have thought it to be. It is the bright children who are retarded, and the dull children who are accelerated. The remedy is to be sought in differentiated courses (special classes) for both kinds of mentally exceptional children. Just as many special classes are needed for superior children as for the inferior. The social consequences of suitable educational advantages for children of superior ability would no doubt greatly exceed anything that could possibly result from the special instruction of dullards and border-line cases.[27] [27] See Chapter VI for further discussion of the school progress possible to children of various I Q's. Special study of the I Q's between 70 and 79 revealed the fact that a child of this grade of intelligence _never_ does satisfactory work in the grade where he belongs by chronological age. By the time he has attended school four or five years, such a child is usually found doing "very inferior" to "average" work in a grade from two to four years below his age. On the other hand, the child with an I Q of 120 or above is almost never found below the grade for his chronological age, and occasionally he is one or two grades above. Wherever located, his work is always "superior" or "very superior," and the evidence suggests strongly that it would probably remain so even if extra promotions were granted. CORRELATION BETWEEN I Q AND THE TEACHERS' ESTIMATES OF THE CHILDREN'S INTELLIGENCE. By the Pearson formula the correlation found between the I Q's and the teachers' rankings on a scale of five was .48. This is about what others have found, and is both high enough and low enough to be significant. That it is moderately high in so far corroborates the tests. That it is not higher means that either the teachers or the tests have made a good many mistakes. When the data were searched for evidence on this point, it was found, as we have shown in Chapter II, that the fault was plainly on the part of the teachers. The serious mistakes were nearly all made with children who were either over age or under age for their grade, mostly the former. In estimating children's intelligence, just as in grading their school success, the teachers often failed to take account of the age factor. For example, the child whose mental age was, say, two years below normal, and who was enrolled in a class with children about two years younger than himself, was often graded "average" in intelligence.