The belief that a class group, when once formed, must operate as a unit within the school prevents adequate adjustment of pupils to the difficulties of their learning tasks. Such would not be the case if the class groups were adjusted to the scholastic abilities of the pupils. The traditional practice of grouping children for instructional purposes is based on the false assumption of the existence of abilities, attainments, and capacities which are common to all individuals within the group. The use of the grade as a basis for grouping, which is by far the plan most prevalently used, is supported by the assumption that all pupils within the same grade have similar capacities for learning and equally developed abilities and skills for performing the learning tasks of each and every subject within the grade curriculum. Life relates many variable factors within and about the growing and learning child. These variables reduce the common elements in the outcomes of learning. Much evidence is on hand to show that, in reality, a pupil usually achieves at two or three different grade levels whenever an achievement battery test is given to him. Scores in various subjects, when interpolated into grades, show such typical variability as 6.0 in reading; 5.5 in spelling; 5.0 in geography; 3.7 in language; 4.6 in arithmetic; and equal variability in civics, history, literature, and other subjects. Such scores indicate that the pupil is not only at the fifthgrade level but that he is also at the third-, the fourth-, and the sixthgrade levels. In this case it is obvious that the pupil should not be given the fifth-grade course of study in all subjects but should encounter the course of study in each subject at a point where his capacities and previous scholastic achievement promise optimum development-especially in the case of the sequential, or vertical, skills subjects.