The purposes of this study were 1) to investigate the power of the one-way ANOVA test after transforming it with large sample size data by using Real Data and 5 sample sizes (30, 60, 90, 120 and 150 students) to see if any differences exist between the tests and 2) to test which method yields the most suitable result at which sample sizes. The samples consisted of 3,600 Mathayomsuksa students in Thailand and used multi-stage random sampling. The instrument for the study was a questionnaire about democratic child-rearing with a score reliability of 0.719. The findings explain the effectiveness of the one-way ANOVA test