Changes in primary students’ mathematical reasoning following open-ended advanced organizer instruction in fraction learning

Mathematical reasoning enables elementary students to explain ideas, justify arguments, select strategies, and conclude. This study examined fourth-grade students’ mathematical reasoning after fraction instruction integrating an advanced organizer with open-ended tasks. A quantitative, pre-experimental one-group pretest–posttest design involved 206 students from two public elementary schools in Semarang, Indonesia. Instruction comprised four phases: preparation, Advance Organizer presentation, learning tasks, and cognitive reinforcement. Students completed a 10-item essay reasoning test before and after instruction and a 20-item response questionnaire afterward. Mean reasoning scores increased from 65.62 (SD = 18.95) to 75.17 (SD = 15.85), a 9.55-point gain (p < .001). The standardized mean change, calculated using pooled pretest–posttest standard deviations, was moderate (d_av = 0.547); the paired-difference standard deviation was unavailable. Seven reasoning indicators improved, whereas deductive, systematic, and consistent reasoning declined. Questionnaire responses averaged 89.08% of the maximum score (“very good”). These findings suggest preliminary within-group improvement but do not establish causality without a comparison group. The study offers a replicable sequence that activates and organizes prior knowledge before open-ended exploration, comparison, and justification in fraction learning.