Page:Popular Science Monthly Volume 85.djvu/570

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 The base line divisions represent one year in age, while five of the vertical divisions equal one school grade. The average mark for each grade may be determined by assuming that the first division of the grade represents a standing between 50 and 60 per cent., 2d between 60 and 70 per cent., 3d between 70 and 80 per cent., 4th between 80 and 90 per cent, and 5th between 90 and 100 per cent. The degree of pitch of the line shows the relative amounts of increase of absolute increments for the same individual.

The main educational corollaries which logically follow from this study would require that our school systems, public and private, be graded on the physiological age and the accompanying stage of mental maturity of boys and girls in place of the chronological age, as is now