Again, my experience with public schools has been extremely negative, but it may also depend on when you went to school. I was in 4th grade in 1969 and I have no memory of learning anything about the slaves other than they were the major reason behind the civil war, and that slavery was a Bad Thing. Even if I had learned this, I don’t think I would have assumed that in the almost 40 years since then there had been such low black immigration, since I also doubt we were taught anything much about British owned Africa.
Where you went to school would also make a difference. I went to grade school in a very poor area and one thing I do remember is that our enclyclopedia was from the mid 1940’s. We were taught to read, write, basic math and basic history - I remember very clearly the extreme difference between my first grade school and the one I attended when my father finally graduated college and got his first decent job.
The condition of the public schools here are a whole different thing.