Mercer Island High School

Mercer Island High School is a roomy senior high in Mercer Island, Washington, run under Mercer Island School District. The school teaches 1,439 students in grades 9 through 12. Enrollment runs roughly 151% bigger than the state mean of about 573.

Across the 6 schools in Mercer Island School District (3,993 students total), Mercer Island High School accounts for its share of the district's footprint.

On demographics, Mercer Island High School lists that the most-represented group is White (52%), with the rest of the student body spread across multiple groups. Other groups include 25% Asian, 13% multiracial, 7% Hispanic. That composition is broadly in line with King County as a whole.

Looking at school resources, On paper, Mercer Island High School has 76 full-time-equivalent teachers, translating to a class-load average of around 18.8:1. The state averages around 21.6:1, so this campus is tighter than the state norm typical. Around 7% of the student body qualifies for free or reduced-price meals, a commonly cited indicator of low-income enrollment. Set against King County (around 38%), the school's rate is south of typical.

After controlling for student poverty, Mercer Island High School performs roughly as the BeatsExpectations model predicts for a school with this FRL share. The predicted value is around 75.5%, the actual is 76.6%, a residual of +1.2 points.

In the surrounding community, the surrounding county (King County) records that the typical household earns roughly $124,746 per year, about 57% of the adult population holds a bachelor's degree or above, and roughly 5% of residents live below the federal poverty line. In all, King County runs 544 public schools (combined enrollment of about 278,492 students), of which Mercer Island High School is one.

Nearest neighbor: Northwood Elementary School, around 0.2 miles off. 8 of the 8 nearest public schools sit inside a five-mile radius. Among the 9 schools in that immediate cluster with test data (this one included), Mercer Island High School ranks 4th on composite proficiency, above the local average of 75.7%.

The campus sits in a commuter-belt setting.

Trend over the last 7 years. Mercer Island High School's enrollment has shrank 5% since 2018, when it stood at 1,521 (now 1,439). White enrollment moved from 70% to 52% across the same window. Class-load math has narrowed: from 20.1:1 in 2018 to 18.8:1 in 2025.

In the discussion threads here, the page collects discussion, questions, and updates around school events, parent volunteer needs, and clubs. Parents, students, alumni, and staff are welcome to weigh in.