For detecting such children, in addition to the tests given above, elaborate tests for individual examination have been devised. The most widely used is a series known as the Binet-Simon tests. A special group of tests is provided for the children of each age. If a child can pass the tests for his age, he is considered normal. If he can pass only the tests three years or more below his age, he is usually considered subnormal. But a child's fate should not depend solely upon any number or any kind of tests. We should always give the child a trial and see what he is able to achieve. This trial should cover as many months or years as are necessary to determine beyond doubt the child's mental status. SUMMARY. Just as we differ in the various aspects of body, so also we differ in the various aspects of mind. These differences can be measured by tests. A knowledge of these differences should aid us in grading, classifying, and teaching children, as well as in the selection of occupation and professions for them. Mental traits have some degree of independence; as a result a high degree of one trait may be found with low degree of some others. CLASS EXERCISES 1. Many of the tests and experiments already described should have shown many of the individual differences of the members of the class. The teacher will find in the author's _Examination of School Children_ a series of group tests with norms which can be used for a further study of individual differences. 2. The tapping experiment described in the first chapter can now be repeated and the results taken as a measure of reaction time. 3. You should now have available the records of all the tests and experiments so far given that show individual differences. Make out a table showing the rank of each student in the various tests. Compute the average rank of each student for all the tests. This average rank may be taken as a measure of the intelligence of the students, as far as such can be determined by the tests used. Correlate this ranking with standing in the high school classes. It will give a positive correlation, not perfect, however. Why not? If your measures of intelligence were absolutely correct, you still would not get a perfect correlation with high school standing. Why not? 4. If you had a correct measure of intelligence of 100 mature people in your city, selected at random, would this measure give you an exact measure of their success in life? Give the reason for your answer. 5. Of all the tests and experiments previously described in this book, which gives the best indication of success in high school?