Some schools may be able to offer young people at 16+ the chance of enrolling on a specific course in school as an adult returner. This would be likely to form part of a package and might include a college placement or a work-based placement.
It would be usual in such situations to apply to the secondary school for the catchment in which you reside. The usual contact would be the Headteacher in the first instance.
Skills Development Scotland may be able to provide further informal information.
For a list of all schools in Highland visit: Schools in the Highlands