1384 
number of minutes, required by a group of the same sex for the 
achievement of the same sex for the achievement of the task, we 
obtained an experimental value, comprising the quantitative data 
regarding time and mistakes. From these experimental values it 
appears that boys always work better than girls. At 8, 9 and 10 
years of age the difference is not so great. It is very conspicuous 
however for the 11-, and 12-year old children. The improvement 
in the work of 8—12 year old children is 58 °/,. 
5. Among boys from 9—10 years a slowing is observed in the 
regular progress; among the girls it appears a year later. 
6. The percentage of quick workers increases regularly as they 
grow older for the boys and girls separately and for the two sexes 
collectively ; that of the slow workers decreases. The advance from 
slow to fairly quick workers is among the boys (with the exception 
of those from 8—9 years) invariably less than the advance from 
the fairly quick-, to the quick workers. Among the girls, on the 
contrary, the advance from the fairly quick-, to the quick workers 
is most marked only from 10—11 and from 11— 12 years. 
7. As regards the number quick workers among boys of 8 years, 
the boys have the better of the girls. This superiority lessens later 
on; then the boys from 9—10 years are on a par with girls of 12. 
The same applies to the number of slow workers. Among the boys 
of 9 years e.g. there are fewer slow workers than among the girls 
of 11. Boys between 10—11 years are on a level with girls of about 
12 years. 
8. With one exception the accuracy of working decreases at each 
age for the boys and girls separately and for the two sexes collectively. 
The increase of accuracy in the five years is largest among the 
girls; it augments with the speed of working. 
9. For the quick-, the fairly quick, and the slow workers among 
the boys a slowing of the regularly increasing accuracy is observed 
from 9—10 years; for those among the girls a year later. 
il. 
In the Proceedings of the Meeting of Feb. 26. 1921 *) we published 
under the same title the results of an inquiry into the phenomena 
of attention, appearing during persistent labour. We now present a 
sequel to it in a number of data concerning the types of workers 
that acted as experimental subjects. For the technique and the 
arrangement of the investigations I refer to our previous publication. 
1!) Verslagen van de Kon. Akad. v. Wet. Wis- en Natk. Afd. Dl. XXIX, blz. 1077. 
