The infants and toddlers program can come to your house or child care center and evaluate your child and provide activities to stimulate him to reach the appropriate developmental milestones. I'm quite sure that there is a significant percentage of the population that would be considered 25% delayed at one point or another under the age of 2, so I wouldn't freak out over that "diagnosis," it just means that there will be a lot of activities given to you to stimulate making up that 25%. Such as tempting him to sit up by placing a rattle or toy in front/above him while he is on his back and "helping" him sit up, or such as placing him on all fours and supporting his stomach. I like to place a boppy behind the child, sit across from him with his favorite toy, wrapping your legs around him until your feet support his back and slowly push the boppy away, making sure you are securely supporting his back with his feet, a little tricky, but what will hold his attention more than mommy (and his favorite toy)?
You know your child best and are his best advocate. I would hate to see a situation like those described by two other posters go unnoticed because your doctor blew you off, so good for you for pushing!
A mother's instincts are very valuable, but everyone should also be careful not to project expectations on children based on "what other children his/her age" are doing or even on their own previous children. Each child is an individual and develops at his/her own rate. Occasionally, children start out slowly and then skip a milestone altogether and jump right to the next one or meet milestones completely "out of order" of the norm/general group of children. (i.e. some children NEVER CRAWL) Usually, Peds tend not to worry until the age of 2. Once a child is 2, particular milestones should have been met, regardless of order or length of time in each stage.
That being said, my Ped. always ASKS ME what is going on with my child, do I have any concerns anything I've noticed that's good/bad/indifferent? If you don't have open communication with your Ped. where s/he makes your concerns and accomplishments feel recognized and validated, then I agree it is time to change your Ped. and/or see a specialist in addition to the I &T prog.
I'm not trying to sound like I know everything and anyone can feel free to disagree with me and any and all of you can choose to ignore my input altogether. (I do however have a BS in Early Childhood Education and have worked with children of all abilities for 8 years now. So, there is a "school of thought" and experience behind my ramblings...)