They call them wonder weeks cause you wonder what the hell is wrong with the kid that week!!! lol . It's a period where the brain is working overtime on a new process like crawling, walking, speech, etc and the child is unusually cranky, upset, clingy for no other apparent reason.

Have a read here: Parenting and Child Health - Health Topics - Wonder weeks

I foud them to be pretty acurate to within a week or so. I think the older the child is the longer the "week" is but the longer between them also. I am wondering if they still have them after 1year but havent read it anywhere yet.

The good news is that the usually have a "sunny week" after when they kinda go "AHHH that's better" and are super pleasant and happy, having accomplished whatever they were working on.

take care,
Sazz