By law the public school system,upon parental request and consent, must provide FREE developmental screenings/evaluations. These developmental areas should address speech, hearing, vision, socialization, motor, and cognitive skills. If the child meets the eligibility criteria, they must provide services, even for 3 and 4 yr olds. Go online to IDEA Part B services and this will let you know what you should expect. If you want services, contact your local school district's Special Education/Services coordinator(if they have someone else handling 3&4 yr old svcs they should tell you) to request a screening. Remember to review IDEA because the school has a timeframe of compliance. If you go this route, you need to know the law and be your son's best advocate! As a parent you have alot of rights, just stand up for them. Good luck!
Often such feedback from day care or pre-school is worth listening to, because those folks (if they are seasoned) have such a range of experiences from which to draw. It can be hard to discern at times what might be difficult but nonetheless 'normal' behavior vs. symptoms of a disorder. Here's what I'd suggest: (a) obtain details about your son's functioning at school; the particulars are important; (b) have a consult with a child mental health clinician who can both 'eyeball' your son and have a discussion with you about him.