Reducing school energy costs has become an important issue, while the energy saving should consider different school systems and student backgrounds. This study investigated the impact of student demographics on energy consumption in elementary and secondary schools and explores the difference of energy consumption in different types and levels of school systems. Data were collected from 3672 schools (including 3108 elementary and 564 secondary schools, respectively) in Ontario, Canada. The number of students whose first language is not English, the number of students who receive special education services, the number of school-aged children who live in low-income households, and student learning ability are all inversely proportional to energy consumption; student learning ability has the largest negative impact. The partial correlation between student enrollment and energy consumption has a trend of gradually increasing as the grade levels increase in Catholic elementary schools, Catholic secondary schools, and public secondary schools; however, the correlation shows a gradually decreasing trend with the increase in grade levels in public elementary schools. This study is helpful for policy-makers to clarify the energy implications of various student backgrounds and the energy consumption difference in different types and levels of school systems to facilitate their formulation of effective policies.