64 American Statistical Association. 



weigh less tlian the boys of Grade II, and these again are 

 lighter than the b()3's in higher grades. 



When children of the same age and, nearly as possible, of 

 the same class of societ}^ are weighed, and the weights dis- 

 tributed by school grade, it is found that tliey follow the law 

 established for the whole material irrespective of social con- 

 dition. Tables are given in Growtli of St. Louis Clvihh'eii 

 of the weights of tlie daughters of manual tradesmen and of 

 the daughters of professional men, distributed by school 

 grade. The results of this study of the weights of girls from 

 the same social class confirm the conclusion that successful 

 pupils are larger than the unsuccessful. 



The relation between the ability to succeed in school work 

 and the rate of growth or yearly increase in size is treated in 

 Tlie Physical Basis of Precocity and Dullness^ p. 176 et seq. 

 It appears that the comparative rate of growth of dull, 

 mediocre, and precocious children of the same sex is the 

 same at all ages, from 7 to 16, inclusive. The data at liand 

 were not sufficient to decide whether this law is true of other 

 ages in the period of growth. It is further shown that the 

 acceleration in weight preceding puberty takes place at the 

 same age in dull, mediocre, and precocious children ; and 

 that the point in the period of accelerated development at 

 which girls become heavier than boys is the same in the dull, 

 the mediocre, and the precocious. 



The following are among the data given in Growth of St. 

 Louis Children : The median and average value of each 

 series of observations ; the probable deviation ; the probable 

 error of the average ; median nunus average value ; relation 

 of weight, span of arms, etc., etc., to height standing ; the 

 5, 10, 20, 25, 30, 40, 50, 60, 70, 75, 80, 90, and 95 percentile 

 grades; the absolute annual increase of the average; the 

 absolute amiual increase at various percentile grades; the 

 relative annual increase ; and several cranial indices. 



