The main aim of this study was to examine the internal structure of a self-developed instrument “the adolescents’ school motivation measuring tool” instrument for use of adolescent school. Exploratory quantitative research approach, and its design was grounded within the exploratory type. A total of 489 school-going adolescents completed the questionnaire. A principal component factor analysis with varimax rotation confirmed the four-factor structure of the adolescents’ school motivation measurement tool, while confirmatory factor analysis was performed to establish the appropriateness of the instrument. The findings established that each of the factors, had good internal reliability values 0.88%, 0.87%, 0.87%, and 0.81% respectively. The SEM model of school motivation confirmed that the factor structure was a good model as the RMSEA (p = 0.066) was significant at a high level. Further, it was also affirmed that inter-correlations existed among each of the components: cognitive and success motivation (r = 0.95); cognitive and social motivation (r = 0.73); and success and social motivation (r = 0.73). Low correlation existed between the components of social and failure avoidance motivation (r = 0.03). This study concluded that the four factors are appropriate measures of adolescents’ school motivation tool for the use of school-going adolescents.