Hi, Marion
I know you�re looking for a text, but when I read about what you needed I remembered the film Play it Forward (2000). Then I tried to find comments about the idea of the film, but I�m not very good at searching on the Internet, so instead I found this 5- minute-video:
https://www.youtube.com/watch?v=X3ld9_p2bS0
Maybe you could do some little writing tasks with it, like thinking of a title, imagining they�e one of the characters involved and descibing what they feel, making up a little story where a chain of favours would develop... Well, it�s up to your imagination!
Well, If I find something more like a text for a reading comprehension or I can think of any interesting idea I�ll let you know. It is an issue which certainly should be considered "hot".