The study sought to investigate the perception of stakeholders on teachers' assessment effectiveness in secondary schools in Port Harcourt Metropolis in Rivers State. Three research questions and one hypothesis were formulated to guide the study. The study adopted survey research design. The sample of the study consisted of 20 principles, 30 vice principals, 150 secondary school teachers and 300 students drawn through stratified sampling technique. Teachers Effectiveness Assessment Scale (TEAS) was used in collecting the data for the study. Simple percentage, mean, regression analysis and Anova were used in data analysis. The result show that stakeholders have different perception about teachers' assessment effectiveness and also that awareness and implementation of best practices in assessment, construction of assessment tools and utilization of information from assessment tools for diagnostic purposes have positive values with the criterion variable (teachers' assessment effectiveness).