"Learning software development without a teacher" is not totally accurate. There is no regular teachers, like a lecturer feeding students knowledge (at least for Holberton School). Students have to dig in and make their own knowledge, and confront it with their peers. Mentoring is very important, by staff or people from the industry. I know there is a lot of mentor at Holberton, I guess 42 must have something like it.

What's really important is to experiment and do real work in "normal condition". That's how you become operational and ready to bring value to a company. Go for it.