An Oral Proficiency Interview (OPI) is a standardized, global assessment of functional speaking ability.
The third stage, known as "Probes" shows the interviewer what the interviewee cannot do, and finds the lowest level of performance which they are unable to sustain for prolonged periods of time (ceiling).
An effective OPI will show an interviewee what they can and can't do with their speech in the target language.
The fourth and final stage, known as the "Wind-down," is designed to ease the interviewee and bring them to a comfortable level of speaking.
[3] The levels of ACTFL’s scale can be conceived as an inverse triangle, with the “Superior” rating at the top representing a wide range of skill in linguistic structures, vocabulary, and fluency.
The Novice Low category forms the bottom point of the triangle, showing little functional knowledge of the language.
In addition to presenting both test takers and test users with a significant time and finciancial burden, some researchers have also noted that the ACTFL OPI is limited by the fact that its scores are based on a series of subjective statements, rather than empirical measurements of linguistic performance.