How does self-esteem affect academic achievement?

My original research question revolved around using music in the classroom to improve student engagement and focus. Once I got into my classroom and met my tutee I realized that there was a better research question. During the first RTI meeting the teacher mentioned that my tutee seemed to really work hard but on assessments appeared to have some testing anxiety. After finding this out I decided that it would be better for me to change my question to look at self confidence and how that would affect her.