This report, written in Finnish with a 10-page summary in English, concerns research on the interrelationship between Piagetian operations, various aspects of information processing capacity and mathematical thought processes and strategies related to number and measurement. In a theoretical discussion, Piaget's research on mathematico-logical thinking in the light of information-processing theory is discussed. In the experiment, 35 first-grade pupils were interviewed individually; the tasks presented to them are described. Piagetian abilities appeared to predict arithmetical performance and especially strategies. Information processing capacity appeared to be closely tied to specific content. Sequence skills were also reported to be related to arithmetical performance, as well as to Piagetian abilities. (MNS)