Children’s strategies for addition and subtraction gradually change from using their fingers and counting to extracting answers from memory. Then, automate it so that calculations can be performed with faster reaction times. However, it is not clear at what grade level the automation will be completed. In this study, students in grades 1 to 4 in a regular classroom were given an addition and subtraction task and their responses and reaction times were measured. The results showed that children in grades 2 and above were not sufficiently automatic in their calculations of addition and subtraction. In addition, the difficulty level of each formula was clarified, and suggestions for effective teaching methods and systematic teaching were obtained. Furthermore, the characteristics of children with calculation difficulties were clarified, and the importance of early support was found.

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The developmental changes using the Sentence Verification Technique （SVT） tests, which were able to assess the three different levels (the surface form, the text base, and the situation model level) for text comprehension based on Kintsch’s model, were investigated in Japanese elementary school children. Then, the relationship between the text comprehension ability and working memory capacity was examined for 2nd-, 4th-, and 6th-grade students （N=114） in study 1. As a result, although the text comprehension ability and working memory capacity increased with the grade in school, the correlation between them was not observed. On the other hand, the text comprehension ability was significantly positively correlated with vocabulary for 2nd- and 4th-grade students （N=68） in study 2. Especially, their vocabulary size affected text processing at the situation model level, which requires the integration between text information and prior knowledge. These results suggested that children's vocabulary size enhanced by various experiences including book reading might facilitate reading comprehension activating prior knowledge.

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[in Japanese]

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