Kinder im Schul- und Vorschulalter setzen sich mit Problemen der Seriation, der hierarchischen Klassifikation, der Mengen- und Volumeninvarianz auseinander und zeigen die von Jean Piaget beschriebenen Unterschiede im konkreten Denken.

The development of thought, beginning at around early school age, is described using original experimental conditions as laid down by the Geneva psychologist Jean Piaget. The film shows how the ability to think operatively - with its essential characteristics of reversibility - makes possible the acquisition of stable classificatory and relational concepts as well as invariability (number, substance, quantity).