This quantitative study investigates the influence of teachers' emotional intelligence on student achievement in an American curriculum international school setting in Bangkok, Thailand. Amidst concerns over student proficiency levels in the United States and Thailand, the study aimed to identify whether teachers' emotional intelligence is linked to a difference in student achievement in reading, language usage, and mathematics. The study responded to calls for further investigation into how teacher emotional intelligence may influence student achievement to inform hiring practices and teacher training priorities to improve educational outcomes. The study aimed to contribute to debate on how to enhance student achievement, addressing a gap in the literature on the role of teacher emotional intelligence in students' educational success. Using Bar-On's theory of emotional intelligence and measurement instrument, the EQ-i 2.0 questionnaire, to measure teacher emotional intelligence, these findings were correlated with student growth data from Measures of Academic Progress (MAP) assessments in reading, language usage, and mathematics. A one-way ANOVA was employed to analyze 89 teacher-student data sets, including 33 reading teachers, 34 language usage teachers, and 22 mathematics teachers, to determine any potential difference in student achievement for those taught by teachers with high emotional intelligence compared to those taught by teachers with low emotional intelligence. The researcher analyzed the data first by considering teachers' overall emotional intelligence and repeated the analysis for each of the composite scales of the EQ-i 2.0 questionnaire, self-perception, self-expression, interpersonal, decision-making, and stress management. Additionally, analyses were conducted to consider the attributes of teacher gender and age for each research question. The findings did not indicate any significant difference in student achievement for those taught by teachers with high versus low emotional intelligence, overall or in any composite scale area. Given the results of this study, it is contended teacher emotional intelligence need not be a key priority in seeking to improve student achievement. Future research recommendations include expanding the sample and settings to further validate and generalize results. It is also suggested to expand the scope of study to include other factors that may be influenced by teacher emotional intelligence beyond student achievement. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]