知的障害児における繰り下がりのある減法の習得過程

本研究では、知的障害児が繰り下がりのある減法を習得する過程を分析し、指導との関連を検討することを目的とした。対象は、小学校知的障害特別支援学級に在籍する６年生の女児１名。指導は、算数の時間に計７回実施した。指導では、お金の種類についての学習、1000円は100円９枚と10円10枚に両替できること、解答が誤答の場合は、なぜ間違えたのかについてその理由を児に尋ねることなどを行った。半具体物を用いて1000－（商品代）を示した後、具体物を操作しておつりを計算するよう求めた。分析は、教師が提示した問題に対する児の解答の正誤、誤答の場合は、児が誤答に至った理由を言語化した内容、解答にかかった時間をもとに行った。その結果、1000－３位数のうち、減数の百の位および十の位が０以外で一の位が０の問題について、第５回目までは誤答が続いたが、第６回、第７回は正答となり、解答に要した時間も短くなった。半具体物を用いた式の提示、および、児が具体物の操作をして解答したことにより、10の補数概念が促進され、繰り下がりのある減法の理解につながったと考えられた。

The purpose of this study was to analyze how children with an intellectual disability acquire subtraction calculation with borrowing using concrete objects. The subject was one girl in the 6th grade who is enrolled in a special needs class at an elementary school. 7 guidance sessions were given during math class. Guidance consisted of learning about types of money and how 1000 yen is made up of 9 100-yen coins and 10 10-yen coins. If a wrong answer was given, the reason for the wrong answer was inquired of the subject. Using semi-concrete objects, equations 1000 - (merchandise price) were shown and the subject was asked to calculate the change using concrete objects. Analysis was conducted based on the right or wrong of the subject’s answer to the problem given by the teacher, verbalizing the process of the subject’s reaching the wrong answer, and the time it took to reach the correct answer. As a result, of the equations 1000 - a 3-digit number, for problems in which the subtracting number was 3 digits or 2 digits other than 0, 1 digits was 0, wrong answers were given until the 5th time. However, right answers were given for the 6th and 7th time and the time required to reach the correct answers decreased. By presenting the equation using semi-concrete objects and by the subject reaching the answer using concrete objects, the concept of tens complement was promoted, leading to the understanding of subtraction calculation with borrowing.