I think the book would be a great supplement to a history class.  It definitely would give students a perspective on thinking at the time.  The book also has literary merit, and is not as simple as it first seems.  English classes can use it to tie in to American history.

Uncle Tom's Cabin should be studied as an important historical work in the Abolition Movement, but only in excerpts at the grade school level; there is just not enough justification to dedicating the time that it would take in class to teach that novel when you think in terms of what the students could take away from it.  Most school curriculums overlook Stowe's book in favor of more approachable texts that have more literary value, like Huckleberry Finn. Like post #2 pointed out, Stowe's novel was influential in its own time, but has lost resonance with more modern audiences, whereas Twain's novels have stood the test of time. 

As a reader of American literature, I am certainly glad that I’ve read Uncle Tom’s Cabin. It is an important piece of writing that reflected something important about our country.

However, as a high school English teacher, Uncle Tom’s Cabin is not a book I would choose to teach in class. That doesn’t mean I wouldn’t recommend it to serious students, but I wouldn’t design a unit around it or spend class time discussing it at great length. I feel this way for several reasons:

1. The book has a certain degree of unrealistic sentimentality. Although Tom is an admirable character, he is too pure to be believable.
2. The term “Uncle Tom” has come to have a very negative connotation that might make it difficult for some students to understand the author’s intent in creating the character.
3. The racial divisions in books like this can cause a lot of controversy in class and among parents and members of the community. Use of the “N” word is often misunderstood and not taken in its historical context.
4. It’s too long to teach it effectively in a high school class. There simply isn’t enough time to  spend so much of it on one book.

I would like to note that teachers who do take on the task of teaching this book have my admiration and professional respect, especially with regards to numbers 2 and 3 above.

http://www.enotes.com/uncle-toms-cabin/summary