The phrase low functioning is pejorative, despite the fact that it is widely used in behavioral health. In my opinion, short of conducting a standardized functional assessment, the phrase low functioning is nothing more than a value judgement that clinicians place on a person in services.
Low functioning is a value judgement cloaked in official sounding clinical jargon. From my vantage point, when a clinician refers to a person as low functioning, they are saying more about themselves than the person they have ascribed that phrase to. When using the phrase, clinicians are saying, "I have failed to realize the unique gifts and talents of this individual". In my experience, the remedy is to get out into the community and see the individual in many different settings with many different friends, family members and natural supporters. When we take the time to do this, new profiles of strengths, talents and gifts emerge. Nobody is low functioning.
Another insidious effect of the phrase low functioning is that we begin to internalize it. If we overhear powerful mental health or hospital staff referring to us as low functioning, we often take that in. It lowers our self-esteem. It errodes our belief in our worth and value as human beings. It wounds us. Eventually we are faced with recovering, not only from emotional distress, but also from this iatrogenic wounding.
Finally, once we have heard powerful staff using the phrase low functioning, we are likely to use it on our peers. For instance, it's not uncommon to hear, "Oh, that program is for low functioning people" or "I don't want to go there. Only the low functioning go there." It's such a sad thing for peers to judge peers in this way.
Low functioning is a wounding and destructive phrase. Though cloaked in clinical sounding jargon, it's time for us to strike low functioning from our vocabulary and instead focus on discovering people's gifts, talents and strengths.