When I studied Othello at school, we were taught that Desdemona, while being portrayed as a spirited woman, was merely a theatrical device to show off the tragedic action and conflict between the male characters. Therefore she was a blameless victim and of sideline interest in the play.
Nowadays I presume that some modern teachers would blame Desdemona for a lack of communication with her husband, and for her inability to calm his jealous and suspicious nature.
Also, she married Othello knowing that his origins were not within the court scene of the time and that her courteous ways might be interpreted as flirtation by her husband, as he did not understand that her manners were simply a means of being pleasant by social graces. This lack of understanding ended up in Iago being able to manipulate Othello for some unimaginable reason.
I think this modern approach to teaching does not fully explore the writings of tragedy at the time of Shakespeare, which sought to explore vital flaws at the heart of man. One of Shakespeare's great talents was that he developed each character (even minor characters) so that Desdemona is a believable person in her own right, so that the audience can relate to the action as it unfolds.