This research is a study of Mathematics learning activity on Addition, Subtraction, Multiplication
and Division of Whole Numbers by using the Problem-Based Learning Approach. The study aimed at: 1) to compare academic achievement before and after learning activity, 2) to compare academic achievement with 70 percent criteria, 3) to study the students’ satisfaction towards the learning activity. The population was 190 Grade 4 students of Anubanphraboromrachanusorndonchedi School in the academic year 2020. The 42 sample was selected by using simple random sampling method. The tools used in this research were 1) 10 lesson plans 2) 23 Mathematics academic achievement tests 3) questionnaire on satisfaction towards the learning activity. The collected data was accomplished on academic achievement test scores before and after the instructional treatment. The statistics used in data analysis were Mean and Standard Deviation and the hypothesis was tested by using the statistical tools. The findings of the research were as follows: 1) The achievement in Mathematics after receiving the instructional treatment with one variable was higher than before receiving the instructional treatment with statistical significance at .05 level. 2) The achievement in Mathematics after receiving the instructional treatment with one variable was higher than 70 percent with statistical significance at .05 level.
3) The Grade 4 students’ opinions towards the instruction were at a high agreement level.