Summary:
ZIP code 98040 includes six public schools serving Mercer Island students from prekindergarten through 12th grade: four elementary schools, one middle school, and one high school. All are part of the Mercer Island School District, ranked first among Washington’s 238 districts in the supplied data. Together, the schools enroll about 3,993 students, and every school has a five-star rating. Overall, this is an exceptionally strong school area, with consistently high achievement across elementary, middle, and high school grades.
Mercer Island High School is the strongest secondary school, ranking second among Washington high schools and reporting a 96.1% graduation rate, a 1.3% dropout rate, and 2025–2026 proficiency of 92.71% in ELA, 79.81% in math, and 88.59% in science. Among elementary schools, Lakeridge Elementary School ranks highest, with 91.35% ELA and 88.39% math proficiency. Island Park Elementary also ranks among the state’s top elementary schools and leads the local elementary schools in reported science performance. West Mercer Elementary is particularly strong in math, at 86.54%.
Islander Middle School is improving steadily in statewide rankings and remains well above state averages, although its science result trails the district average. Northwood Elementary School is still strong compared with schools statewide but is the main area for closer attention within Mercer Island. Its 2025–2026 ELA and math results were 72.73% and 75.14%, respectively, below the district averages; fourth grade was the clearest concern, with 65.38% ELA and 64.29% math proficiency. Some science scores are suppressed, so those results cannot be fairly compared. For families comparing schools, Lakeridge and Island Park stand out among elementary options, while the district’s high school results are particularly impressive.
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