My eldest eventually chose the public school diploma system over 100% unschooling, but we did continue with the documentation throughout her teen years as a back-up, should completing the high school diploma requirements prove counter-productive. (She was only enrolled in school part-time and was travelling extensively and living away from home.)
What I did was to keep a fairly rigorous-looking private blog, paired with a database system for her transcript. I used Blogger for the blog with Zoho for the transcript, though there may be a better system now. I logged her "courses" according to course number and name, description, comments, start and completion date, course level and credit weight. Here's a sample.
|Social Studies 9
Canadian geography and history, geography and culture of South-East Asia.
Travel to Edmonton (9 days), Montreal (9 days), across Canada's heartland by rail (4 days) and to Southeast Asia (60 days).
Background reading, tours, museums, planning, collaborating with others on trip planning. Photo- and text-journaling.
Excellent photo and powerpoint
presentations with discussion x 3.
Where I live (Canada) it's the transcript that matters. No one ever asks to see a diploma, but it would have been easy to generate a diploma based on the transcript.
The blog was really just some brief anecdotal documentation that supported the awarding of each "credit" on the transcript. For Instrumental Music 11 I linked to YouTube videos. For Social Studies 9 I put in a few photos of her in Myanmar, Thailand, Montreal. For Math10 I documented the textbook she had worked through. I tagged the posts by course name so that they were easy to sort through. The blog would serve as a very robust portfolio if she were to apply to university as an unschooler.
As it turned out our local high school was happy to award her credits under their system for her unschooled learning, based in part upon my documentation of it. But I think the system would have worked well also as in support of an application for higher education.