In this response, I will outline several ways of answering this question. As you will see this question has no definitive answer.
Single-Session Therapy and One-At-A-Time (OAAT) Therapy are Synonymous
Hoyt (2011) introduced the term ‘one-at-a-time’ into the SST literature and it has been used by some as a term that is synonymous with single-session therapy. That is they both describe the practice where the therapist and client set out to help the client in a single session on the understanding that the client can choose to have more sessions if they elect to do so.
Single-Session Therapy and One-At-A-Time (OAAT) Therapy are Different
Some therapists see SST and OAAT therapy as different. Of these, some prefer the term, ‘one-at-a-time' therapy to the term single-session therapy. When asked why, these therapists argue that the term, ‘SST’ stresses the single-session nature of the work, while the term ‘OAAT therapy’ stresses the fact that more therapy is available even if this one session at a time. Services based on OAAT therapy principles allow clients to have further session but only, as the name implies, one session at a time.
Services based on OAAT therapy
In some agencies, OAAT therapy is introduced in an attempt to offer clients help at the point of need and to reduce the time it takes for clients to access counselling. Usually, this is response to the usual practice of offering clients a block of sessions, most often six, a practice which neither reduces waiting lists nor brings down waiting time appreciably. In these agencies the term 'one-at-a-time' is interpreted literally and clients can only book one session at a time. However, in these agencies, there is no cap on the number of sessions a client may have - although as noted above these can only be booked on at a time. Indeed, some clients may have in excess of six sessions if they choose to do so.
In OAAT services clients are encouraged to reflect on what they learned from a session, to digest this learning, to take appropriate action and to let time pass before they decide to have another therapy session. In this way, clients can get the most from every session that they elect to have.
Services based on SST
In agencies that offer SST services, in my view there is more flexibility. As we have seen, in OAAT therapy agencies, clients can have more sessions but these can only be booked one session at a time. In SST, by contrast, if clients elect to have further therapy they can choose from the services that the agency offers. Thus, they may elect to have a) another single session after the first, b) a block of counselling sessions if these are available and clinically indicated c) ongoing therapy if offered and even d) specialist services if the agency offers them itself or has an arrangement with an agency that does. What is important here is that the therapist is transparent with the client concerning what help is available to the client after the first session and what is not.
Therapists’ Preferences
I argued at the beginning of this response that SST and OAAT therapy can be regarded as synonymous terms. They both describe the practice that the therapist and client set out to help the client in that session knowing that more sessions are available. In my experience, therapists who prefer the term ‘SST’ place most emphasis on the first part of this sentence, i.e. helping the client in one session. By contrast, therapists who prefer the term ‘OAAT therapy’ place most emphasis on the second part of the sentence, i.e. further help is available. OAAT therapy is therefore a term acceptable to counsellors who have doubts, reservations and objections to the single-session intention of ‘single-session therapy’.
Whether SST and OAAT therapy are the same or different, what is important is for the person using the term SST or the term OAAT therapy to make clear how they personally are using these terms rather than rely on generic definitions.
Reference
Hoyt, M.F. (2011). Foreword. In A. Slive & M. Bobele (Eds.), When One Hour is All You Have: Effective Therapy for Walk-in Clients, (pp. xix-xv). Phoenix, AZ: Zeig, Tucker, & Theisen.