Semester school

A semester school is a school that complements a student's secondary education by providing them with the opportunity to step out of their regular school for half an academic year and step into a uniquely different educational setting while continuing their required academic studies. The academic curriculum at semester schools tends to be college preparatory, interdisciplinary, and experiential.

Attending a semester school can:

The first semester school was Milton Academy's Mountain School which opened in 1984 in Vershire, Vermont. Since then more than a dozen additional semester schools have opened across the United States of America and in other countries. The list of opening dates below shows the growth in semester schools over time and their geographic diversity.

...
Wikipedia