I call it controlled crying but what we are just trying to do is help our daughter to self soothe. Our daughter is breastfed and has always gone to sleep on the boob. Because of this she is unable to self soothe when she wakes in the night. I am still feeding her during the night but sometimes she has woken an hour later after being fed and we have had to go in to her to get her back to sleep as she obviously doesn't know how to do so herself.
So what we have started now is to soothe her by not picking her up. We rub her belly and shush her. We leave her for a minute or two and then we go back and try again with the belly rub and shushing. Sometimes we do pick her up just in case she needs a burp (even though she has already been burped) and then put her back down to try again.
Let me make it clear that we are not just letting her cry it out till she stops. We are trying to soothe her without picking her up so she doesn't rely on it.
We are just after some thoughts about whether this is too early. A lot of information that we have read says controlled crying should not be done before 6 months or 9 months old.