What Can a Highschool Student Work on After They've Completed the Course?
If a student has completed the Raspberry Pi + Python Standard Course, the next step would be to purchase the Level C lessons or the Level C+D lessons to continue to learn more skills.
If your student has completed the Raspberry Pi + Python Complete Course, the next step would be to purchase the Level D lessons to continue to learn more skills (and build a robot).
If your student has completed the Robotics Course, here are some suggestions. Since the course introduces students to programming, electronics, and robotics, its helpful to figure out which was their favorite part. Here is what I would recommend based on that answer:
Programming - There is a lot more to Python than we could cover in our course so something like CodeAcademy.com might be a good place to start. They don't really cover interfacing with electronics circuits like we do but they can teach you how to do everything else. There are so many things you can do with Python and they cover a ton of them.
Electronics - Unfortunately, we don't know of any other resources like ours where you get sent parts and curriculum for advanced electronics projects. The only thing we can really recommend here would be finding interesting projects that are documented online, like on YouTube, and building some of those until they're ready to look at high school or college level courses. If a local school offers any sort of electronics course then that would be a great option too. Some members of our team were able to go through an electronics course when they were in high school, but unfortunately a lot of these programs have been cut in the last few years.
Robotics - You might see if there is a FIRST robotics club in the area. FIRST robotics teams build robots to compete in challenges that change each year like this. Even if it's there is nothing close to you, your closest FIRST team might be able to recommend age-appropriate resources that are available in your area.
You might also look for a local STEM or STEAM center. They're popping up all over the place to promote getting more kids into technology. They might have ideas on local resources as well.