The district built Eastridge High School in 1957 and 1958. The school opened its doors for the 1958-59 school year for ninth and tenth grade classes. In the next two years, 1959-60 and 1960-61, successive ninth grade classes entered the school, bringing the building to a full 9-12 capacity in the 1960-61 school year. The students who had entered as tenth graders in 1958-59 became the first Eastridge graduates three years later, in June, 1961. The students who entered as freshman in 1958-59 and graduated in 1962 became the first class to attend a full four years at Eastridge.
In 1985-86, the district reorganized the use of space within the Eastridge structure, to provide a separate junior high school area to serve the specific needs of students in seventh and eighth grade, within an eastern wing of the school. Students continued to share the cafeterias, auditorium, library and other central areas of the school.
Enrollment decline turned into steep enrollment growth during the later 1980s, when birth rates began to rise again as the baby boom generation became parents. Affordable housing, amenities that the community offered and a district focus on improvement in programs, services and student achievement attracted young families to East Irondequoit. Growth continued swiftly throughout the 1990s into the first years of the 21st century. Enrollment in East Irondequoit grew at one of the fastest rates in Monroe County during this time period, from a low of approximately 2400 in the mid-1980s to more than 3500 as the century ended.