Abstract
The main purpose of the present study was to examine the developmental processes involved in understanding of the concept of crowdedness. More specifically, it focused on the qualitative understanding of equal distribution and the interrelations of number, length, and crowdedness. Adolescents (11 to 17 years old, N=369) participated. The results revealed that in these youth, development of the understanding of crowdedness followed a U-shaped pattern. Understanding of the interrelation among the three concepts of number, length, and crowdedness was plateau in the 11 to 14-year-old. When it developed, the youths' understanding of equal distribution and the interrelation between 2 concepts temporarily dropped. However understanding of those matters improved in the 17-year-old participants, in whom reconstruction progressed. It was also found that qualitative understanding of the concept of crowdedness developed in the 16- and 17-year-olds, but it was not fully acquired even by the 17-years olds. The present findings suggest that development of qualitative understanding of the concept of crowdedness proceeds after 14 years old.
