Is my bipolar disorder why the quality of my school work can be so drastically different?

Yes : If your bipolar disorder is not well controlled your ability to focus and concentrate could change depending on your fluctuating mood. For some patients their 'manic' phase reflects more an agitation, irritability, lack of focus and scattered thoughts. As it changes to a more ' depressed mood" there may be lack of interest in school work which would affect focus and concentration also.