I have recently released a Python Course on Primer[1]. It is interactive, incrementally guided and completely free for Python-I.
You can checkout the content of the course without signing up as it is also an online book. [2]. The book is around 440 pages and it will take mostly 12-15 hours for your son to complete. And you can understand where he is getting it wrong by reading and analysing his conversations. (For an easier way to do this, Multiplayer mode is in roadmap)
Benefits of using Primer:
- Automatic flashcards generation
- Personalized Book generated at the end of the course from conversations, notes and questions
- Stores conversations so that he can revisit and resume after giving up for a while.
Its a bit new platform therefore, I have written an introduction post about Primer as well which you might find interesting. [3] [4]
EpicPython seems to have an integrated Python environment which is definitely something of a plus as it makes it easier for a learner. Primer doesn't have that as it is intended to solve a different problem altogether.
On a sidenote, I will very happy if your son chooses Primer to learn Python. Its less than a week since I launched Primer.
[1]: Primer Website: https://primerlabs.io
[2]: Python-I Online Book https://primerlabs.io/books/python-i/
[3]: Introducton to Primer Blogpost: https://primerlabs.io/blog/introducing-primer/
[4]: Introduction to Primer Comics Based Blogpost: https://primerlabs.io/comics/introducing-primer-comics/