Students’ mathematical idea is very important in learning mathematics. Many studies had proposed learning activities to promote learning performance focusing on mathematical ideas of the addition topic. However, those studies lake of innovation to improve students’ learning of addition. This study applied lesson study and open approach as innovations to improve students’ learning of addition by focusing on mathematical ideas. This study aimed to analyze first-grade students’ mathematical ideas of addition in the classroom using lesson study and open approach. This study employed a qualitative research method. The target group was 76 first grade students, the demonstration school of Khon Kaen University, Thailand. Data were collected by fieldnote taking and photo recording of students’ written works. Data were analyzed by content analysis according to Isoda and Murata (2011). The results of this study found that first-grade students’ mathematical ideas include 1) count all 2) count on 3) make ten as a unit of counting and addition 4) decompose of addend for addition 5) decompose of augend for addition and 6) decompose both of addend and augend for addition.
Naphaporn Woranetsudathip, Khon Kaen University, Thailand