In A Raisin in the Sun, why does Beneatha say that she is not on assimilationist and what does she mean?

Beneatha says that she is not an assimilationist in Act II Scene 1.  At the beginning of the scene, Beneatha is wearing the Nigerian traditional garb that Joseph Asagai has given her as a gift, and she is dancing to traditional music.  When George arrives to take her out on a date, Beneatha gets into an argument with him about his upper class values which she deems as "assimilationist."  By this, Beneatha means that she thinks that George has lost touch with his ancestral African roots and that he has conformed to American societal standards (here she implies that these standards are racially bound and based on "white" culture).  Beneatha thinks that she is more well-rounded person because she claims to understand her heritage.