If it's a seasoned therapist who charges a fortune, I don't do a gift, but might have my child write a sweet holiday note. I am pretty sure I helped put one therapists kid through college and she drove a very fancy car, she does not need a gift card.
If it's a therapist who takes insurance and is good, might do a gift card and than you note.
Through the schools, I only gave a gift if the person was good.