My only personal experience would be that my DS seemed to be waaay behind on talking until he turned 2. It was a HUGE source of frustration for (both) of us. It caused major tantrums on his part because he couldn't communicated his needs. He's a feisty, active, passionate, extreamly sensitve child which also made for a difficult toddler-hood. I would constantly have conversations w/ his DC provider who (in her wisdom) would assure me that many kids are more like my DS than EVERYONE elses kids that seemed to be fully conversational by the time they were 2!! I never did schedule an assesment for him and wouldn't you know his speech took off just after he turned 2? Now at 4 YO he never shuts-up!! LOL!
It's hard not to worry, I still do. There are times when I just don't know what's going on in his head, when I quiz him on his ABC's he'll skip letters, or quickly loose interest. When he counts he always misses the #15 for some reason and he gets easily frustrated. I worry how he will do in school, and for this reason I will hold off another year before I start him in kindergarden.
Now my sister on the other hand from the almost from the time her DS was born felt something was wrong w/ him. I can't tell you how many IEP meetings she went to, how many Dr's Psychologists, school counslors and many other "professionals" she'd talked to. If you spend a few hours or even a day or so w/ my nephew he seems like a normal kid, but a mother can tell, who spends more time with a child than the mother? He had SO many dignoses labled on him and even taken several meds. No one supported my sis thru all this, everyone kept telling her he was fine, a "typical" boy. After years of this she, after much persistance, finally got an order from her Dr. and school to have a study done on him at UCLA. After several days and a panel of Dr.'s and psychologists they conculded that he had what they are calling a "mixed nureological development disorder." He didn't fall into any catagory, but displayed many charateristics of many different disorders. She felt vindicated when she recieved a very thick report from the study proving that she was right. It was hard accepting something was wrong w/ the child, but after many years at least she had answers.
I guess what I'm trying to say is it's normal to worry about your child, Lord knows I do, esp. w/ the family history of my nephew! You can go thru a barrage of tests and meetings, and still not have any 'real' answers. I think it's a good idea to get an early intervention test done, but it's not an end all to everything.
It was hard for me to accept that there could be anything wrong w/ my nephew, for in doing so I would also have to accept that there might be something wrong w/ me, and there could be something wrong w/ my children. But I realized that everyone has something wrong w/ them. We are all unique individials, God made us special each in our own way and even the "negitive" things about ourselves can be a positive. The Bible says men intend things for evil, but God can use them for good (not an exact pharaphrase). Wheither it's genetic, enviromental, emotional, developmental, we all suffer from the same condition: the human condition.