The purposes of this research were to study the opinions of teachers in High Schools under the Secondary Educational Service Area Office 17 toward teamwork and compare the results by school size and work experience. The sample used in this was a group of 304 teachers under the Secondary Educational Service Area Office 17. The sample size was determined by Kerjcie and Morgans table and stratified sampling. The instrument used in this research was a 5-rating scale questionnaire that had a discriminate on index of between 0.41 and 0.90. The reliability was 0.96. The data were statistically analyzed using: percentage, mean, standard deviation, t-test, one-way analysis of variance (One-way ANOVA) and Scheffes method was used to compare the pairs. The findings of this research were as follow: 1) The opinions of teachers in High Schools under the Secondary Educational Service Area Office 17 toward teamwork was at a high level overall and in each aspect. 2) The opinions of teachers in High Schools under the Secondary Educational Service Area Office 17 toward teamwork, when compared by work experience, was not statistically significantly different. 3) The opinions of teacher in High Schools under the Secondary Educational Service Area Office 17 toward teamwork, when compared by school size was statistically significantly different at the .05 level.
