You might need more research in the form of interviews or background data; alternately, you may wish to re-interview the subject of your story to fill in some blanks.
Four months later the reasearchers re-evaluated the students'progress through a combination of school data, teacher ratings and in-depth interviews with students and parents.
Four months later the researchers re-evaluated the students 'progress through a combination of school data, teacher ratings and in-depth interviews with students and parents.