* Junior high typically encompasses grades 7-9 (or sometimes 7-8), and often has a more departmentalized structure similar to high school, with students changing classes and having different teachers for different subjects. The focus is often on preparing students for the academic rigor of high school.
* Middle school usually covers grades 6-8 (sometimes 5-8), and often emphasizes a more integrated, interdisciplinary approach to learning. There's a greater focus on social and emotional development alongside academics, with teachers sometimes teaming up to teach multiple subjects.
Essentially, junior high is a more academically focused transition to high school, while middle school incorporates a broader developmental perspective. Many schools now use "middle school" to describe the same grade levels previously known as "junior high," often reflecting a shift in educational philosophy. So while they can overlap significantly, the terms aren't perfectly synonymous.