In what ways could the study of foreign languages in school be improved?

In a recent thread, a jelly pointed out that the best way to learn a language is to have been born to parents speaking it. This is undoubtedly true. It may not be the fastest way, but it definitely yields the best end results.

I’m from Germany. When I was ten, I moved to Korea with my family. I went to an English school. Within a year, my sister and I were almost caught up with native speakers of our age. “Immersion” seems to have been at work, and it worked like a charm.

While now, as an adult, my vocabulary is much less expansive than the typical native speaker’s, the time in Korea did guarantee me effortless As in English for my remaining school years.

Considering how many hours schools spend teaching their students a foreign language, shouldn’t results be more impressive? How could this work?