ask your pediatrician of anyone that they may recommend in the area. Preschool can be pretty intimidating and my son was showing anxiety at school as well and all of a sudden he is doing great(a few playdates with classmates later, and maturing.) He was the youngest in the class and the kids were so much older. It could be something at the school such as an unruly classmate or pressure to perform or just the separation. What does he say when you ask him?Did the people who examined him see him in the classroom setting. My guy is quite different at home where he is very comfortable and other places that he feels safe and comfortable in his extra activities. Most teachers if bring something up to a parent really have a concern and care. Part of who our children aree is how they are born, he is probably a very sweet, observant, cautious boy, can be shy or timid in unfamiliar situations and probably shines in otheres. It is not the only child thing so dont go there. If you ever go into the class for special days you will see all kinds of nervous behavior on part of all different kids. some who are not anxious at all can show the same behavior and some will surprise you ..even at birthday parties this is evident. SOme professionals will go to classroom and observe students and talk to teachers so they can see the thing she is concerned about in the setting on their own may not see it at all. Good luck!