Effects of problem-based English writing instruction on Thai upper secondary school students’ critical thinking abilities and argumentative writing skills

The objective of the study was to examine the effects of problem-based instruction on the critical thinking abilities and argumentative writing skills of Thai upper secondary school students. The researcher constructed a 10 weeks’ training program in a Thai secondary girls’ school in Bangkok. The sample group was 46 M6 students. The instructional instruments include lesson plans, various instructional materials, and topics. The research instruments include writing assignment critical thinking test and a writing scoring rubric. The data were analyzed using paired t-test with SPSS. Cases of students’ writing were analyzed qualitatively according to argumentative writing score rubric and critical thinking test indicators. The results of the analyses revealed that 1) sample group students gained significantly higher average scores on the critical thinking post test than the critical thinking pre-test at the significance level of 0.05 with a mean difference of .674. The t-value is 2.821, and the effect size is 0.26 which was a medium effect; 2) sample group students gained significantly higher average scores on their fourth argumentative writing assignment than the average score of their first argumentative writing assignment at the significance level of 0.05, with a mean difference of 1.261. The t-value is 13.967 and the effect size is 0.7 which is a large effect. The case’ analysis supported Problem-based English writing instruction to be an effective way to improve students’ critical thinking abilities and argumentative writing skills.