im 17 and about to go to college. i havent believed in a god for a really long time. My mom always drags me to church at every chance she gets, and I've even tried to lend hits, like asking her about the bible's hypocrisy.
If you are comfortable telling your mom, then honesty is definitely best. And explain to her calmly and positively that you don't believe in god, and why. You might also mention that you aren't judging her for her beliefs and nothing about your relationship has to change.
Being honest with her will be best for both of you. Just tell her the truth next time the topic comes up. Sh will probably react like my parents. Somewhat disappointed, but overall accept it. She may ask why or what happened. For me it was proof, history & science. But you can insert your answer there. Be sure to explain the you have been an Atheist for some time now. Some people almost think you've suddenly transformed to a monster when you tell them. But if you explain that this is no new news and they realize you are still you and have been, she will be better about it. Also big, is telling her you don't judge her for her belief's and perhaps explain some of the false stereotypes of Atheism. Whatever you do, don't try to de-convert her. If she shows an interest in you explanations, you can delve deeper. But don't actively pursue it. Hope that helps.
I'm going to play the devils advocate here (pun intended)
You are going away to college, man. She's probably under enough stress from that as is. If she is really religious (and dragging your ass to services at any chance indicates she probably is) it's only going to upset her. Remember, religion tells her that you are going to HELL. You are DAMNED. Parents that take it well probably aren't all that certain in their faith, but ones that are....for them it's worse than saying you have terminal cancer.
She's your mom. Smile. Go along with it. You don't know how long you'll have her. Accidents happen every day. If you are going away to college, it isn't like she'll be able to drag you to church once you leave. Keeping her happy is worth the occasional inconveniences when you visit back home.
There will be times later, when she won't be so anxious. There will be times without huge life-changing events like moving away.
Tell her when she doesn't already have so much to worry about.
Hi. I'm going through the same sort of thing right now and I'm going to agree with misty on this one depending on how religious your mom is. I generally think honesty is the way to go. However, I told my parents when I became an agnostic and they FLIPPED OUT. I've always been a pretty good kid, I never really got into trouble and now they think I'm "on the wrong path" and they "don't know where they went wrong." The conversation (which evolved into a three hour shit storm) pretty much ended with them telling me not to ever tell them anything like that ever again, they'd rather just not know. Now, as much as this pains me, because I'd much rather them accept me for who I am rather than pretend like I'm something I'm not, I'm just going to respect their wishes because they will never understand. Now I've gone from agnosticism to atheism and if I told them, I think that they would try to have me committed. It sucks. But it helps me to know that there are tons of kids out there in my shoes. Every situation is different, but that was mine. Hope everything goes ok.... :)
Obviously what you should do depends on the kind of relationship you have with your mum. But I'd probably swing towards Misty and Mandi's side of things. Sometimes honesty doesn't work with parents. They are way too emotionally wrapped up in your life to see things rationally. They take things really hard if things aren't going well with their kids.
Show them that you are still a good, moral, motivated person through your actions and achievements. Show them that they've done a good job bringing you up. Work hard at college etc. Then come back and express your doubts gradually. Give them the good news about your marks or whatever, to butter them up, then tell them what have to tell them.
That's what I did and it worked out fine.
If you've already gone through with it, I'd be interested to know how it went. My cousin is in the same position as you and she asked for my advice. Not entirely sure if I was correct in what I told her to do (same as above).