Go ahead and put it on your resume, no one's going to stop you. Having heard of some of the stuff that people put on their resume's that they supposedly do, your case is in some ways even funny. You actually do this tutoring, whereas you get a lot of people that put big things on their resumes that they have never even contemplated doing/being part of. I remember reading of someone who put on their resume that they were the president of some moderately sized charity. Anyway it turned out that the interviewer was the real president of that charity, so lets just say they didn't get the job.
So mate, go ahead and put it down, and congrats on being so helpful/considerate. You will find that there are a lot of people like you on here, who give up their valuable time to help the rest of us out.