I have a practice makes perfect song that we sing together, just a silly little thing that reminds us that we aren't failures, we just need to keep practicing. Nobody jumps on a 2 wheeled bike and takes off on the first try ever.
I would take a mental note of it....I'm aware that sometimes children "quote" people more on what the child feels or perceives the person is saying more than what they said. If a teacher stood over my child in front of the other kids in class and said "You're not good, you need to practice" (in anything but kung fu, where the teacher is very very strict), I would probably get my panties in a bunch for sure. (Not that she's wrong but that it was not the way to say it). But the truth of that story may have been something as simple as kneeling at the desk and having a little talk with him, and saying that reading may be hard and feel like you're hitting a wall right now, but keep practicing and you'll get better as long as you practice. Who knows? If my son was struggling and came home with that story (he's come home from pre-K with something similar), I would request a little meeting with the teacher and not be accusatory or confrontational, but say "___ told me ___. I assure you we ARE working on it daily, he's really working hard at it, but he's still struggling a bit. What are you doing in class, and what do you suggest I do at home, so we can work together as a team to help him best?"
In doing so, you're doing a few things at once: 1) you're letting the teacher know what you've heard, that you communicate with your child about school, and you are an active mom who has no problem coming to school, in a peaceful, more productive way than getting the teacher on the defensive. 2) you're letting the teacher know that you're working on this, and what you're doing, and that you are up for teamwork. you can actually get some neat ideas on how to improve or best use the time you spend on reading at home. 3) you're showing that while something might be a mild annoyance, your main concern is your child. his education, how he feels about himself, how he operates in class, etc. teamwork is a good thing. 4) you can feel the teacher out and listen to your instinct on whether the teacher has your child's best interest at heart and was just misunderstood, or whether there's a bullying problem (that's actually pretty rare, in my opinion, but we saw recently on yahoo news a couple instances where the bullying was real). 5) you're showing your son that you have his back, and helping to build his confidence. you may also get more information than what your son is divulging about what's happening in the classroom.
good luck! just be encouraging and supportive.....he'll get it!