Keep detailed records of your students' progress and the areas in which they need help. Refer to these records when talking to parents.
Display your certifications. This is a subtle, but effective reminder to parents of your qualifications.
State the positives about your students as well as the areas that need help. Use a criticism sandwich: state a positive, the area that needs help and another positive.
Remain calm and listen to the parents' concerns.
Look the parents in their eyes, and stand and sit at the same level.
Remind the parents that your primary goal is to make sure that their child succeeds.
Be cognizant of your tone and body language. These things will often cause more of a reaction than your actual words.
Avoid accusing the parents. State your observations and facts.
End the meeting if the parents become too impertinent.