Supporting students to justify choices : a problem-solving mathematics lesson study

Abstract

This report presents a lesson study conducted with Year 4 primary students to strengthen their mathematical reasoning and justification skills within a budgeting context. The lesson centred on a realistic scenario in which Mrs. Green aims to create a healthy breakfast hamper with a €25 budget. Students worked in groups, each adopting a character from a concept cartoon – Sally, Maze, Tina, or Finn – who presented different suggestions or challenges related to the hamper’s contents. Using a justification fan and a familiar problem- solving mat, students critically evaluated and justified their assigned character’s choices, with one group tasked to independently design a suitable hamper. The activity was carefully structured to engage students at varying levels of mathematical ability and encourage the use of precise mathematical language. Observations and group presentations revealed how the structure of the task supported deeper reasoning and reflection. The lesson was purposefully selected due to previously identified students’ difficulties in articulating mathematical justifications. This report outlines the lesson study process and discusses how the approach helped foster critical thinking, collaborative learning, and clearer mathematical communication.