This study was concerned with effect of large class on teachers’ lesson delivery and students’ classroom participation in junior secondary schools. The instruments for data collection were two instruments known as relationship between large class size to standard class size questionnaire (RBLCSSCSQ) and challenges of large class size on teachers’ lesson delivery questionnaire (CLCSTLDQ). The questionnaires were developed by the researchers, validated by three experts and used for collecting data from respondents. Fifty (50) junior secondary school teachers from five government junior secondary schools at Abuja Municipal Area Council of Federal Capital Territory in Nigeria formed sample of the study. Two research questions were answered and two null hypotheses were tested. The data were analysed using mean percentages and bar charts to answer the research questions. One of the cogent findings of the study was that large classes dominated junior secondary schools and teachers were faced with different problems and challenges while delivering lessons to students in large classes. Other findings of the study established that 90% of teachers found it difficult to achieve classroom control and management, 68% of teachers found it difficult to start lessons on time, 96% of teachers found it difficult to attend to individual students’ need, 86% of teachers found it difficult to notice student absenteeism, 78% of teachers found it difficult to end lessons on time, 54% of teachers found it difficult to identify students by name, 88% of teachers found it difficult to evaluate students at the end of the lesson, 92% of teachers found it difficult to assess students at the end of the lesson, 70% of teachers found it difficult to instil discipline on stubborn students during lesson and 94% of teachers found it difficult to walk round the classroom space during lesson. The paper concluded with various relevant recommendations such as adoption of 30 students per teacher policy and establishment of new junior secondary schools.

Keywords : Effect, Large classroom, Challenges, Teachers, Students.