In school I've learned about every other continent or at least part of its origin or culture. I have never taken a regular high school class where they teach anything about the history or Africa beyond the continent's involvement with slavery. the only classes I've know to teach about African countries are very advanced classes. So why is this? Is this just the school I went to?
It might just be the school you went to. I have a distinct memory of my 7th-grade world history class spending a few days on the Mali and Songhai empires.
Such survey courses, however, necessarily leave a lot out. I doubt you learned much about South America or southeast Asia beyond the US's involvement there in the 20th century. You probably learned very little about central or eastern Europe past the Byzantine empire, and almost nothing about Russia.
I think the unfortunate reality is that high school history curricula have to fit a lot of information into a relatively short amount of class time. there are certain events, domestic and international, that more directly impact the place we live in. Not saying that African history isn't important, fascinating, complex and relevant. But learning about World War II is prioritized over, say, the Mali empire, because it is necessary to explain America and its place in the world today. Whereas if you learned about the Mali empire instead of WWII, you would be lacking a lot of context for 2015 American geopolitics. We should learn more about African history beyond its conquest. But the question is, what do you remove from the curriculum to fit it in and how do you justify its removal?
I think it's just your school. My 10th grade history class covered not-North-America and not-Europe that year. I remember there being pictures of Great Zimbabwe.