ABSTRACT
The present study aimed to investigate (1) the development of probabilistic reasoning before formal instruction, measured yearly from 3rd grade preschool to 3rd grade elementary school and (2) the role of early numerical abilities measured in 2nd year preschool and vocabulary knowledge, measured at the beginning of 3rd year preschool for probabilistic reasoning. For the present study, 292 children (150 girls) were longitudinally followed from preschool (M
age = 4y10m) until the 3rd grade of elementary school. Probabilistic reasoning abilities were assessed by evaluating children’s performance on three tasks: (a) distinguish certain from uncertain events, (b) compare probabilities, and (c) create equal probabilities. Children grew steadily regarding all probabilistic reasoning tasks (i.e., distinguish certain from uncertain events, p < 0.001, η
2
G
= 0.31; compare probabilities, p < 0.001, η
2
G
= 0.42; create equal probabilities, p < 0.001, η
2
G
= 0.14), but the growth occurred later on the third task. Furthermore, early numerical abilities predicted children’s ability to compare probabilities, and early vocabulary knowledge predicted the performance across all three probabilistic reasoning tasks and the growth in the ability to create equal probabilities.