Abstract:
This research aimed to: 1) Develop a causal model of writing ability among High School students under Chiang Mai Secondary Educational Service Area Office 2) Examine the goodness of fit between the developed causal model of writing ability among High School students under Chiang Mai Secondary Educational Service Area Office and empirical data, and 3) Investigate the direct and indirect effects of factors influencing writing ability among High School students under Chiang Mai Secondary Educational Service Area Office. The research sample consisted of 749 High School students from schools under Chiang Mai Secondary Educational Service Area Office, selected through multi-stage random sampling. The research instruments were: 1) An essay writing ability assessment comprising one item with scoring proportions weighted according to the importance of writing ability components, yielding an intraclass correlation coefficient for inter-rater reliability using the Two-Way Random-Effects Model of .960, a difficulty value of .771, and a discrimination power of .217 and 2) A questionnaire regarding factors affecting writing ability, measuring variables including Reading habits, Parental support, Motivation, Teaching quality, Student-peer relationships, and Online social media communication, with an overall reliability coefficient of .969. Data analysis employed descriptive statistics, Pearson correlation coefficient analysis, goodness-of-fit analysis of the causal relationship model of factors influencing writing ability with empirical data, and analysis of direct and indirect effects of factors affecting writing ability using structural equation modeling. Major findings can be summarized as follows: 1. The causal relationship model of factors influencing writing ability among High School students under Chiang Mai Secondary Educational Service Area Office demonstrated good fit with empirical data, with fit indices of χ² = 207.252, df = 176, p-value = .0536, RMSEA = .015, CFI = .997, TLI = .996, and SRMR = .047 2. Analysis of the effects of independent variables on writing ability revealed that Reading habits (β = .658), Teaching quality (β = .716), and Student-peer relationships (β = .659) had statistically significant positive direct effects on writing ability at the .01 level. Motivation (β = .322) and online social media communication (β = .393) had statistically significant positive direct effects on writing ability at the .05 level. Parental support showed no direct or indirect effects on writing ability. All variables collectively explained 39.9% of the variance in writing ability. Furthermore, Parental support and Teaching quality significantly influenced Reading habits at the .01 level (β = .407 and β = 1.205, respectively), jointly explaining 80.7% of the variance in reading habits. Reading habits and Teaching quality significantly influenced motivation at the .05 and .01 levels respectively (β = .353, p< ; .05 and β = .544, p.01), jointly explaining 50.9% of the variance in motivation. Teaching quality significantly influenced Student-peer relationships at the .01 level (β = .493), explaining 87.4% of the variance in Student-peer relationships.