As has been said a couple of times, it is important to teach To Kill A Mockingbird as a novel with a historical context. If a generation is 20 years, it came out over two generations ago. I wasn't yet in high school (generally ages 15-18 in the US) when it was published and I'm now retired.

It is no more correct to use it as an examination of "the effect of poverty on black and white people in the [contemporary] Southern States" than it would be to use Sinclair's The Jungle to study the meat packing industry in present-day Chicago or any of Sayer's books to look at the relationships between the gentry and the working classes in twenty-first century England.