The invested teacher is the teacher who looks at a child and sees the child, unfiltered by any hang ups or triggers that the teacher may have acquired as they have grown up. This means not taking a dislike to a child, not being resentful of a child, because they have a more privileged life than we had, for example, or because they have a particular skill or talent which we wished we had. It means not being dismissive of a child because they do not know how to behave properly, or they cannot grasp simple ideas, or how they dress, or how they hold themselves.
The invested teacher is not resentful, jealous, indifferent, dismissive, superior nor inferior, not boastful, malicious, nor easily provoked.