Summary:
O Fallon, Illinois, has one high school: O Fallon High School, serving grades 9–12 and enrolling 2,540 students in 2024–2025. Its most important distinction is consistent above-state test performance: in 2025–2026, it scored above Illinois in every reported subject and grade.
With only one school in the list, O Fallon High School is both the top and bottom school, so there is no meaningful local school-to-school comparison. Its advantage over the state ranged from 7 to 15 percentage points across the nine test results. The largest leads were 15 points in grade 11 ACT ELA and math; the smallest was 7 points in grade 9 PreACT math, where 49% of students met proficiency compared with 42% statewide. Other reported outcomes were also favorable: graduation was 96% versus 90% statewide, while chronic absenteeism was 22% versus 24%.
Results improved relative to the state overall, but not in every grade or subject: averaged across the nine matched tests, the school’s scores rose about 1 point while state scores fell about 1 point, widening the average advantage by about 2 points. The exception was grade 9 ELA, where the school’s lead narrowed by 4 points; grade 10 science showed the largest widening, by 6 points. SchoolDigger gives the school 4 stars and ranks it 101st of 620 statewide schools (84th percentile) in 2025–2026; it ranked 101st of 698 in 2024–2025. The school’s student-teacher ratio was 16.3:1, and 28% of students were free/reduced lunch eligible in 2024–2025. Since this list contains only one school, it cannot show how the school compares with other local high schools.
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