Though I'm not aware that Khan Academy is specifically designed to address specific learning differences, the beauty is that it is designed to be self-paced, mastery-based learning, making it accessible to as many students, young and old, as possible.  I hope you've found a way to utilize the resources!  

Most parents/teachers find it helpful to have a student get to know how to use Khan by exploring a course that they feel competent in, then working towards course mastery or assignments that meet their specific needs.