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The aims of this research are; 1) To compare the students’ achievement about the Single linear equation of Grade 7 classroom 2) To study the effectiveness after using the STAD 3) To explore the students’ attitude toward the use of the STAD approach for their mathematic lesson. The participants of this research are 40 students from a classroom of Grade 7, Jaruspichakorn School, who study Mathematic in the second semester, 2016 Academic year. The participants are Cluster Random Sampling. The tools for this research are; 15 lesson plans about the Single Linear Equation through the STAD approach, the test of 30 questions with 4 multiple choices with the reliability is 0.75 and the questionnaire with the inferential statistics such as mean, SD (Standard Deviation),t-test (One-Sample Test) and (Paired-Samples Test).
The result shows that; 1) the students’ achievement for solving the Single Linear Equations is 76% higher than the standard 2) the difference between the mean of the students’ achievement for solving the Single Linear Equations before and after using the STAD approach is 8.8 or 67.5% 3) the effectiveness after using the STAD approach is 0.6318 4) Most of the participants agree that the use of the STAD approach for their mathematic lesson help them to develop their knowledge.