Managing a school can only be said to be successful when students succeed. The provision of all resources can only be accounted for by high academic achievement of students in internal and external examinations. In Nigeria, English Language can be described as the link to student’s success and progress in education. It is the means of conveying information in classes, examination and its importance is further emphasised by the requirement in post-secondary education for admission to study most courses. At various workplace, it is the means of discussion among workers from various tribes and is indeed the lingua-franca for the country. Learners’ academic achievement in English language has been adjudged by scholars and researchers to be poor in public secondary schools. Most teachers are still attached to a singular instructional management strategy that favours teacher-centred learning that is book knowledge. This paper investigated the extent to which teacher instructional management strategies, classroom management, effectiveness influenced students’ academic achievement in public secondary schools and suggested appropriate measures to enhance academic achievement. It was concluded that there is a positive relationship between teacher instructional management strategies, classroom management, effectiveness and students’ academic performance in English language since they contributed significantly to academic achievement in public secondary schools. It was recommended among others, that, teachers should be exposed to contemporary instructional management strategies through regular inservice trainings to enhance their teaching effectiveness. Also, adequate instructional resources: text books, tools for practical demonstrations among others should be provided in secondary schools for teaching and learning of English language.