Interleaving subtraction strategies to foster primary students’ strategy proficiency

This thesis explores the potential of interleaved practice to improve primary students' strategy proficiency in three-digit subtraction tasks. An experimental classroom study with 236 German third graders compared the effectiveness of interleaved practice, including between-comparison prompts, with blocked practice, including within-comparison prompts, in teach-ing the adaptive use of different subtraction strategies. Across four articles, this research high-lights the superiority of interleaved practice in promoting flexible and adaptive strategy use. The results show that interleaved practice better fosters students' ability to adaptively select subtraction strategies based on task characteristics than blocked practice, leading to improved problem-solving accuracy. This effect was observed immediately post-intervention and sustained five weeks later, indicating that the benefits of interleaving are long-lasting. Notably, the positive effects of interleaving on adaptive strategy use were found to be independent of students' prior knowledge, indicating its broad applicability across a diverse range of learners. The effectiveness of interleaving was influenced by students' need for cognition. However, this influence did not differ significantly from its impact on blocked practice. Moreover, the results show that interleaved practice helps to reduce overreliance on the standard written al-gorithm and encourages using more efficient strategies, such as indirect addition and compen-sation strategy. Cluster analysis further revealed that interleaved practice predicts inclusion in a high-adaptivity cluster, highlighting its role in fostering comprehensive adaptive strategy use. Additionally, interleaved practice promotes the development of flexible calculators—stu-dents who employ various strategies with few errors. This is in sharp contrast to the blocked condition, which tends to lead to a greater reliance on the standard algorithm with associated errors. This finding highlights the potential of interleaved practice to cultivate a more versatile and accurate problem-solving approach in students. This thesis contributes to the understanding of effective strategy instruction in mathematics. It advocates for the integration of interleaved practice as a means of cultivating adaptive expertise and accuracy in problem solving.