Hola Shirley

The sentence is "... dice que no se puede concentrar mientras estudia"

Here, that "se" is the reflexive pronoun for "concentrarse" (to concentrate) - to concentrate [on something] is used as a pronominal verb in Spanish. 

With verbal structures using an infinitive, the "se" can be placed at the beginning of the structure: "se puede concentrar" (the way it's used in this text) or could also be placed at the end, stuck to the infinitive: "dice que no puede concentrarse mientras estudia".

I hope this clarified it.

Saludos

Inma