My son was 18 months old, uttered only a few words (never in public), was very shy, and did not respond to his name. We were referred to the state's evaluation program (Birth to Three) and he's been tested every three months ever since. All has been normal and he's now 3 1/2. This has been our experience.
A POSSIBLE CAUSE
First and foremost, if your child is having speech difficulties, take a look at child's baby's fenulum (the thin membrane under the tongue than connects it to the bottom of the mouth). It is sometimes too short and makes speaking harder than usual. This often goes unseen/ undiagnosed and is very important as it affects eating & speech.
Most cases are not so readily visible - look to see if the baby can stick out her tongue (stick your finger in - sometimes they push it out). If the tongue doesn't pass her gum line, doesn't stick out past her lips, or if the shape seems odd (like a "w") there may be a problem.
In my son's case it was attached to the very tip of the tongue (extreme - level 1) which made it hard for him to nurse when he was born, though not impossible. It went undiagnosed for a few weeks but when discovered it was easily clipped by a peditrician. It is hereditary - in my case, I was 5 years old and speaking with a "french accent" of sorts before the toungue-tie was diagnosed. Fixing it was a litte more involved, and took general anesthesia, but my speech is fine now.
However, when my son was 18 months, he barely uttered a few words, did not respond to his name and was extremely shy. We were referred to the state's evaluation center (Birth to Three) and he had a number of hearing tests to see if he was OK.
EVALUATION OF MY SON - 18 MONTHS
The first test that was done on my son was hearing, at the local hospital. They are very young so two doctors had him sit on my lap and had gentle noises go off in a soundproof room. If he looked that way, a little lighting bug lit up. He started looking out of the corner of his eye to see if it turned on when there was no sound, but the overall result was that his hearing was better than mine. He wouldn't sit still for a test that involved putting a cone in his ear (to check the inner middle ear) but this is usual and all else looked OK.
We then discovered he wasn't responding to his name because he wanted to be called "B", instead of his regular name. Big mystery solved, stage lasted a few months, now he's quite proud of his name.
We still had to go have the state evaluators come to our house though. Two women came, one stayed with me a little out of his line of sight and asked questions, while another did different tests with him with little toys. The overall result was that he was normally, at the very bottom of the range, but still OK (kids develop at different rates, boys are slower than girls). They gave advice and excercises to follow during the next three months. He did not qualify for any type of therapy (there have to be delays in several areas).
As a side note, I spoke with other moms who were actually trying to get their slow-developing kids into this program because private therapy is very expensive.
At 21 months, we enrolled him in a nursery school. This helped bring him out of his shell and made him more comfortable around kids. The change in him was huge, even though he's still a little on the shy side, just like his dad.
We've been in the Birth to Three Program ever since, not in therapy but in the standard follow up they do every three months to track his progress. He's almost four but we still get questionnaires, feedback, and excercises.
The questionnaires we receive, as well as the excercise (for every stage up to age 5) come from the book "Ages & Stages Learning Activities" by Elizabeth Twombly available on amazon. It's an excellent guide but if you can have professional guidance from your state program, all the better.
This all sounds very scary at first but the testing they do is really thorough and the many activities they encourage actually make learning for the kids (and you) a lot of fun.
