There is great latitude in designing work-study or independent study courses for credit, especially for 16 and 17 year old students. A form can be developed for students who work part time to document their hours of work, the responsibilities they carried, and the skills they developed. Their supervisor/employer can fill out an appropriate part to document their learning.
Also, students can be given credit for completion of independent courses they pursue on their own interest, such as computer technology or auto mechanics. Companies who offer such courses usually offer a certificate of completion which can be copied as documentation for your school’s assigning credit toward graduation. I once had a senior who had earned his PA state vehicle inspection license before he graduated.