My experience was with to a different specialty therapist, but there was also a loss of trust for my son.
A speech therapist through my ds�s playgroup misinformed ds that his parents were telling them he couldn�t talk. This was announced in front of ds, his opinion wasn�t actually solicited, and despite what he was told the judgment didn�t come from us.
(He was 2, teething extremely hard, and was already reading to us but not demonstrating to strangers on command.)
We had 2 weeks of ds bursting into tears, after all we had been telling him up to this point that he was smart. Discipline also went down the tubes because we were obviously jerks.
What helped: Chances to show off. Lots of third party confirmation that the therapist was wrong (and if we actually had been misstating his abilities behind his back, confirmation that so were we. The items below refer to reading, because for him it is a big strength).
1) Dropped that playgroup. New playgroup instructor had much more experience and promptly observed in front of ds that he knew his letters and numbers.
2) New book arrived in the mail, so he was able to prove to us that he was smart, by reading it to us immediately upon opening the package. (He didn�t need to but our credibility with him was shot at this point, so he basically needed opportunities to prove himself to us in his area of strength.)
3) A grandma that he didn�t see often (the impartial observer) showed up showed up and gave him a lot of feedback on how bright he was. Her arrival marked the end of his upset.
She also brought a coloring/activity book whose title indicated anything that a preschooler might know would be contained within, and nothing they tested for at the first playgroup was contained within.
Good luck.
