336 Trans. Acad. Sci. of St. Louis. 
It is a well-known fact that children of the prosperous 
classes are better developed physically than the children of 
the poor. It has been suggested that the children of poor 
parents are not so successful in school work as the children 
of the rich, and that the poor children are compelled to leave 
school at an earlier age than the rich, and for these reasons 
are relatively less numerous than the rich in the higher grades. 
According to this idea, the better physical development of 
the children of the same age in the higher grades, as illus- 
trated above in boys aged 11, is due to the preponderance in 
the higher grades of the well nourished children of the rich. 
This may be, and probably is, a factor in the phenomenon, 
but is surely only a partial influence. 
For when children of the same age and as nearly as possible 
of the same social class are weighed and the weights dis- 
tributed by school grade, it is found that they follow the law 
established for the whole material irrespective of social condi- 
tion. A glance at Plate XLVI, derived from Table No. 36, 
will convince the reader of the truth of this statement. 
