CIO is the only thing that ever worked for my three kids. I don't remember how it worked with my first, but with my second, we had no choice but to CIO. We'd tried the feber method, but it just prolonged the inevitable. I don't remember what age we actually started CIO with her, but I do remember that at 9 months old, my daughter had learned how to manipulate myself and her daddy! After the first time I let her CIO, when I put her to bed she'd cry for maybe 30 seconds and then go to sleep. When her Daddy tried to let her CIO, he couldn't handle it and he'd go get her after just a couple of minutes! So whenever he put her to bed, she cried for at least 45 minutes before her i-d-i-o-t (read: GENIUS) Daddy would go in and try to rock her (she'd just get all hyper and play with him then).... then he'd put her back in her bed and she'd scream another 45 minutes or so before she'd finally pass out (unless he went and got her out again....). They went through that cycle until he finally wised up and quit going in there.
With my third child (10 months old now), we did CIO at around 6-7 months.... the first couple of times we did it was at naptime, because she was still sleeping in our room at night. Fortunately her Daddy knew better this time, so he didn't rescue her, and it only took a couple of times before she got used to sleeping in her crib at naptime. The night time transition was a breeze after that!
CIO is a tough thing to do, but it really is worth it. You aren't abandoning your son, or making him feel unloved, or screwing him up for any amount of time. What you are doing is teaching your son how to calm himself down and soothe and comfort himself. This is a very important skill that a baby needs to learn, and they will become independent and self sufficient because of it. My daughters are as secure and happy as a child can be. They know they are loved and special, they love snuggling with me on occasion (maybe once or twice a week if I let them) while their Dad is gone (he's deployed), but they have no problems sleeping in their own beds either.
Last thing..... CIO is not
a method only used by selfish moms who just want sleep (I have heard that argument too many times to count!). A good nights sleep is absolutely crucial to a mommy.... especially a working mommy! Your son needs you to be at your best in order for you to be able to take care of him properly. CIO not only benefits you in getting you a good night's sleep, but it benefits your son, because it gives him a fully functioning mommy!!! Hope this helps!