It can be rather difficult for a parent to address a problem that arises in school, and even more so when the child is quite young and may not be able to describe what is occurring at school, and how s/he is experiencing school. If you have time to do a little fly-on-the-wall observing of your child's functioning in school, that might be helpful.
In general it would probably be a good idea to thank the teacher for letting you know what's going on, show an attitude of support, and more specifically, say whether or not you have ever observed the particular behavior yourself, or have heard reports of this behavior when your child has been in other settings. Be honest, and avoid getting on the defensive. Do show that you are taking the information seriously and will give it careful thought. The calm tone you used in your question is just right.
Two incidents might or might not point to an actual problem. If you feel there is enough of a pattern, or if you sense that the teacher is at the frustration point, but is feeling kind of stuck about where to go from here, you could try the following:
Ask for a functional behavioral analysis. This could be done by, for example, the school social worker. The idea is to see what contexts this behavior is mostly likely to arise in, and if there is any pattern to the antecedents. Understanding what may be triggering the behavior can be helpful.
Ask that the school occupational therapist (OT) do a consult. The OT can provide insight about the child's sensory processing patterns that may be affecting behavior in school. Also, the OT can provide sensory equipment, such as a bouncy chair, fidget items, etc., that can provide sensory stimulation the child may be seeking, but without causing any harm to anyone.
- Keep your child's primary care provider in the loop.
It is sometimes helpful to offer things like raw carrots, chewable fidgets, frozen sensory items, etc. In the short term (as in this coming Monday), while you're waiting for the other things to fall into place, you could try sending a couple of things to school with your child, and emailing the teacher to let him or her know what you are sending in, and why. For example: there are special erasers that can be put on the end of a pencil that are designed for children to chew on. You can pick up a couple of freezable teething rings in different colors at the drug store, that don't look like teething rings, in the shape of a hand or foot. If you send in two, each in its own baggie, one can be kept in the nurse's freezer, and they can be swapped out as needed.
Make sure you offer these items to your child in a neutral tone, after trying them out at home, e.g. "I'm putting two frozen feet in your school bag, in case you feel like chewing on them during school."
Try to get a feel, from the other parents, whether having a conversation with the principal might be helpful.
My answer is based on my experience working with my child's school to support positive behaviors.
Here is an article that might be helpful: http://www.askdrsears.com/topics/parenting/discipline-behavior/bothersome-behaviors/biting-and-hitting-16-ways-stop-it