I also had a slow learner in one of my groups. What I did is that I personally gave him extra lessons during lunchtime or during recess. I can tell that it does work. In my case it was boy also, and he knew that he had problems and he wanted to do the extra work in order to get better in class. He had long attention span problems also, so I always placed him close to me, in front of the class. In addition, I had him participate by asking him questions and letting him the time he needed to answer. It was harder to deal with this student during exams or tests because he was always slow completing them. I gave him the extra time he needed by asking the other students to read or work on an ongoing project individually.