Typical children develop in typical ways, starting very early in life. There are infant smiles to familiar voices and turns of head when they begin to recognize their name spoken aloud. There's the ability to speak and an interest in various toys. These milestones occur at typical ages (7 months, for example, for baby to respond to her own name) but unless a parent also happens to be a pediatrician attuned to developmental delays, it can be difficult to know what to look for until there's reason to wonder if something is wrong. (Why isn't my 18-month or two-year old talking much? is one such question.)
The rise in autism cases has led to the creation of several web resources to help parents and others with questions:
The Centers for Disease Control has a website devoted to developmental milestones for children as part of an effort to educate the public and medical practitioners about what to look for.
Firstsigns.org has a lot of information about screening and early intervention services. Start at their home page and then check out the page called recommending screening tools.
Who does the screening? You can start with your pediatrician's office, but it helps to look at the checklists on the websites like those above; some pediatricians are a target audience for education and awareness about developmental delays. States like Massachusetts have early intervention specialists who can visit your house and test your child. Again, it helps to compare what you see with your child, his behavior and skills, and how he compares to what is typical on the developmental checklist.
The answers to these evaluations may not lead to an autism spectrum disorder. But whether they do or not, they will help guide you to next steps to take and services to seek to help a child grow and develop.