ARCT , exams etc...

[MusicMom]

I am a small town piano teacher who teaches because she loves seeing kids "get" music.  I have read a lot about certification and having students sit for exams.  Can anyone please give me information on these subjects.  Most of my students come from lower middle class families and just want to have a little culture in their lives, or just want to be able to play for their Sunday services.  Our big excitement is our Christmas Recital in December and the Spring Recital in May.(We actually had it tonight)  
I never took any exams and I doubt if any of my former teachers were certified.  Does it matter? And where would you go for such certification?

Any help would be appreciated.