Abstract: This study examined the development of hypothesis-testing thinking strategies of elementary school children. In a sample of 550 children representing different grades,we obtained the following results. First,Task 1 with multiple probable solutions was more difficult than Tast Ⅱ that contained definite solutions. Second,the development of these children's probability thinking,which was a linear function of age,also differed depending on the probability tasks provided to them. Third,the interaction between probability thinking development and task complexity also applied to the use of successful and unsuccessful problem solving strategies. Finally,to conduct our research,we developed and used a fixed-example procedure. We believe this new procedure is better suited for assessing hypothesis-testing strategies than the variable-example procedure that had been used in the past.

Key words: elementary school child, thinking strategy, hypothesis testing, artificial concept formation