At our school, the final major project done at the end of the year is called a CPT.
This is one of them that i use for grade 9's - but it could easily work with any high school grade level.
It involves creating a mixed media portrait - and designing it so that it contains an element inspired by a famous portrait artists' work.
This project involves a lot of freedom and choice - with regards to who they do a portrait of, what materials they use, how they apply the materials etc.
(I find it important that the CPT is mixed media so they can apply ALL the skills they've learned throughout the semester)
This COMPLETE package includes everything you need:
-An explanation of the CPT and the steps involved
-A research component - where they create a sketchbook page based off their portrait artist
-A final reflection on the CPT and the art course itself
(you could always eliminate this step, but I always love reading them)
-A proposal (2 pages), complete with a timeline for the project that students fill out themselves, to help them with time management.
-An inspiration Powerpoint that goes through examples to help inspire them and get them excited
This takes them 3-4 weeks depending...they turn out FANTASTIC.