Subjects 

Subjects were 84 boys, 12 to 15 years old.

[...] they participated in groups of four. All subjects in a group had the same age.

Procedure

Selection of subjects 

For each session, the four subjects who had to participate were selected at random [...] however [...] they had to be of the same age and from four different classrooms. They were taken from their classroom and brought individually to the experimental room. This room was partitioned in such a way that they could not see each other when entering and there was also no possibility for visual contact during the entire experimental session. Moreover they were not allowed to talk aloud during the experimental session.

When the four subjects were present, they were welcomed by the main experimenter who explained that he wanted to study how children make different kinds of decisions.

Categorization 

Simple random categorization (SRC). Subjects were told that for administrative reasons two groups had to be formed.

All subjects had to write the name of their group on the first page of a booklet that was in front of them.

Simple similarity categorization (SSC). These subjects were also told that for administrative reasons two groups had to be formed.

[...] subjects were assigned randomly to the two groups. They were instructed then to write the name of their group on the first page of a booklet that was in front of them.

Crossed categorization (CrC). The two social categorizations just described were crossed. This was explained very extensively to the subjects using a blackboard on which the group structure was depicted.

These subjects went through exactly the same procedure as the subjects of the other conditions except for the fact that there was no categorization phase.

The two simple categorization conditions and the no categorization condition contained 12 subjects each. The crossed categorization condition contained 48 subjects [...].

All subjects had a booklet in front of them, and for each task that followed they had to use a new page.

Subjects had to fill out four rating scales: three of them were only used to explain how they had to answer these scales, but the fourth one was important. On this scale subjects had to indicate whether the group structure was clear for them or not.

Perceptual ability task

The next task was presented as a task in which they would make a series of perceptual decisions in order to enable us to measure their perceptual ability.

Measurement of dependent variables

Performance evaluation. The subjects were told that they were not the only ones who participated in he study, and that other persons already had participated or would participate very soon.

It was explained then that they had to indicate for each group involved (two in the simple categorization and four in the crossed categorization condition) how well most persons of each group would have performed in the perceptual estimation task.

General evaluation. Subjects were asked to answer three evaluative questions on 7-point rating scales.