sam**, my 16mth old sleeps thru, 7pm - 8am usually, but my 3yr old, well, that's a different story. She wakes a couple of times per night 2 - 3 times per week. We let her cry sometimes, but at the moment, she's getting over a tummy bug, so need to go to her to see what's wrong! I look forward to a good nights sleep soon!
does your baby have a dummy? try putting it on a chain so he can find it himself. We started this when I decided our then 7mth old could do without a feed mid early morning. I didn't go to him when he woke, instead I let him cry. It lasted 1/2 hr of whinging until he gave up, found the dummy on the end of the chain & went back to sleep. The next night, it lasted 15mins, & the next 5. From then on, he's slept thru. Mind you, the cry wasn't a scream for help, a 'mummy I'm starving', or anything like that, more of a cry then turned into whinging noises. Nothing that stressed him too much (or me).
I'd say if you are going to try it, stick to it for 3 nights, if the crying is uncontrollable & doesn't settle or stop, then give up, he's obviously not ready. Try again in a couple of weeks.
Believe me, it's easier tho to do it at the 7-8mth stage than try to get a pre schooler to sleep thru! I wish we'd trained our daughter to do it at that age too!