D., I want to second Dawn's excellent advice, all of it.
I would add that it seems odd to me that the teacher is contacting you about this within the first week of school. Unless your son is truly exceptionally disruptive to the entire class, I would not expect an experienced K teacher to be contacting parents for "not listening in class and ignoring instructions" in the very first week -- because those behaviors are so very typical for K students, especially students who have not had any preschool experience (like Dawn, I wonder if your son had any form of preschool at all?.....). But the teacher should expect and be ready for those kinds of behaviors unless, as I noted, the child is extremely disruptive and distracting, or the teacher is new and inexperienced and doesn't realize that it's not time yet to start telling parents "your child has issues." Or...the teacher, as Dawn said, could be very experienced but so burned out and jaded that she's done with teaching and is there only in body.
Is the teacher a newbie or one with some experience? Or does she perhaps do some kind of "weekly update" for kids at first, and you're hearing what she intends to be just a normal, "kids do this and yours does too" update but you're hearing it as "Your child isn't working out here" instead? Some teachers might make a point of giving all parents a little update, but if you are new to having a child in school, you might be misinterpreting her well-intentioned simple update as an early warning that your son is in trouble.
I would talk to her privately (ensure your son is not there) and tell her: I know that most K kids are wiggly and not great at listening. Is there something beyond that with our son? Is there a reason that, in the very first week of class, we should be concerned, or is this normal getting-adjusted issues? I also like the idea of asking the counselor to observe your son. What you say to the counselor should be confidential; I'd tell her or him that you were worried to be hearing these things in just the first week (especially if your son has no issues at home with listening to you and following your directions).
I am not leaping to "the kid is perfect, so blame the teacher" here, but I do find it unusual that this specific complaint is being voiced so early, when not llistening and not following instructions are typical K issues most of the class might have at first.
If your son did not have any form of preschool -- if he came straight from full-time-at-home with you into a school setting -- then he may indeed have a much harder time at first adjusting to having an adult who is not mom tell him what to do. If you recognize that and help him a lot at home by playing school etc., it will speed things up, but it will still take him longer than it would take children who had more experience of being outside the home and having to listen to and follow instructions from an unrelated adult. That's just normal and he should catch up.