Singing sensation

So I learned the Mozambican national anthem when I first arrived here. (Funny, I lived in France for a year and never learned the French anthem). So anyways, we sing it everyday at school. The kids line up in their turmas (classes) underneath a giant tree (for shade) and face the teachers to sing. Normally I can only really hear the first few rows of students singing. It wasn’t until I was standing to the side of all the students that I actually heard the whole group- they were harmonizing! It was amazing! I’d never heard it before because I’d been listening to the girls in the front, but the boys all were harmonizing in the back. Wow it was so beautiful. I’m trying to think where they all learned to sing like this- is it something they teach in school? Is it mandatory to take singing class? Do they separate kids in grade school and teach them the different tunes? Who knows, but it’s amazing. Today I actually listened for the harmonizing, making sure it wasn’t a fluke from yesterday, and I got chills. They’re beautiful.