I think that anytime a teacher needs to speak with a parent about something that has a sense of gravity to it, the conversation needs to be approached with a sense of care and cation. If a teacher is explaining to a parent that their child has a special need, it might be wise to not open with the classification of "learning disability." To begin with such a term in such an emotionally charged setting helps to put the parents on the defensive and gets them to focus on a particular term as opposed to the plan of action to assist their child's learning. Instead of a proactive discussion, employing the term "learning disability" gets parents to hang their hat on a term or trigger "fight or flight" tendencies. This does not help the discussion.
There should be more than the teacher present. If a child has been tested by another professional, that professional should be present to help the parents understand why the classification is being made. There should be documentation that the parents understand reflect something more than a "whim" has been noted in the child's learning patterns. The teacher should explain what the condition is in the child and also be able to fully address how this will not limit the child's capacity to learn. I think that in such a discussion, parents want to be encouraged that while there is an initial shock to what is happening, there is no cause for alarm or panic. Parents should be given time to speak, in which the teacher becomes more of an active listener who understands and empathizes with the parents. These steps can help parents in a discussion that a teacher leads about a significant change in their conception of how their child learns best.