Formal assessment of students’ learning outcomes occurs mainly in the classroom. The psychological and academic well-being of most learners is hinged on the assessment feedback from teachers to the learners, parents and school authorities. The level of teacher assessment literacy, therefore, determines the competence of the teacher in making value judgment on the behaviour, ability and prospects of a learner. The purpose of this study was to investigate the level of secondary school teachers’ assessment literacy. The survey design was adopted for the study. Two research questions and two hypotheses were tested at 0.05 level of significance. The population of the study comprised all secondary school teachers in Rivers East Senatorial District, Nigeria. Stratified random sampling technique was used to draw a sample of 500 teachers from 10 secondary schools in Rivers East Senatorial District. The instrument used for data collection was: “Teacher Assessment Literacy Test” adapted from “Teacher Assessment Literacy Questionnaire”. The instrument was validated using KR2O and a reliability coefficient of .76 was obtained. Descriptive statistics and ANOVA were used for data analysis. The results revealed that the level of secondary school teachers’ assessment literacy is significantly influenced by in-service training and teachers’ area of specialization. Secondary school teachers’ assessment literacy level was higher among teachers who had been retrained through in-service training. It was recommended among others that more opportunities be given for the retraining of teachers in educational assessment, especially in practical application of assessment processes through workshops and exchange programmes to ensure global best practices among secondary school teachers in Nigeria.