I would certainly be frustrated if I heard a teacher say my child was lazy. I also would recommend looking at why your son is doing the minimum. My daughter not only does the bare minimum, but will convince people that she does not how to do the work. She still tests extremely high, but asking her about her experiences, she is very shy and says that she hates attention being brought to her so she pretends that she does not know it, or will only do what is required. Another child I worked with that was gifted simply wouldn't do the work at all, and when asked he (at age 7) said "why would I do it if I already know how?". It was important to recognize that this child just needed more stimulation and challenging work, while my daughter needs to work on anxiety.