Introduction As practitioners concerned with treating speech-language disorders, one of our primary goals is to accurately and efficiently determine which communication skills should be targeted for intervention. How do we know when something needs to be taught? What defines a skill deficit or a communication breakdown ? In everyday terms, a speech-language problem is signaled when a breakdown occurs in the interaction between a speaker and a listener. That is, we say that communication is successful when the outcome of an interaction is effective (i.e., functional), but when the interaction is weak and ineffective, we suspect a deficit in the repertoire of one of the communication partners. Thus, the critical aspect that defines communicative competence lies in the success of the dyad, a dynamic process comprised of functional units of discourse between a speaker and a listener, even when these roles are assumed within a single individual (e.g., Lodhi & Greer, 1989; Palmer, 1998; Skinner, 1957). Despite the fundamentally social nature of communication, assessment tools for speech-language deficits rarely take into account this requisite speaker-listener unit, nor is it routine to test for, describe, or analyze specific breakdowns in this unit. Most speech-language assessments in widespread today evaluate response topographies (forms of responses) alone, without regard for a functional analysis of the causal variables that lead to the specific topographic features of responses. Indeed, much assessment time and energy is expended in classifying speech-language performance, not by its role within a unit of functional communication between a speaker and a listener (i.e., cause and effect), but instead only by its arbitrarily-labeled categories describing non-function based properties such as word structure (e.g., nouns, verbs, plurals), modality (expressive, receptive), relationship (e.g., antonyms/synonyms, agreement), or other inferred characteristics (e.g., ellipsis, nomination, phonological process). This focus is illustrated by ASHA's (1993) definition of language disorder as an impairment in comprehension and/or of spoken, written, and/or other symbol systems. The disorder may involve (1) the form of language (phonology, morphology, and syntax), (2) the content of language (semantics), and/or (3) the function of language in communication (pragmatics) in any combination. Although function is an element of this definition, this usage of the term refers to a linguistic feature of language (pragmatics) in contrast to Skinner's analysis of function in which environmental variables describe (and thus, define) the contingent relation that accounts for each particular instance of an utterance (i.e., language). As such, linguistic descriptions are less adequate for applied work (i.e., treatments) than is Skinner's model, which specifies the variables that evoke and strengthen verbal behavior. To be sure, a thorough topographic description of an individual's speech-language repertoire may be a necessary component to plan an appropriate therapy program, but it is insufficient to accomplish the task because a key element of the evaluation is missing. Our job during assessment is to document not merely occurrences of wrong responses to assessment items, but also the speaker-listener environment (antecedent and consequent variables) in which the topography occurs. If a functional analysis of the speaker-listener exchange is omitted from the assessment, a critical part of language learning is at risk of being excluded from an effective intervention plan (Damico, 1993; Frost & Bondy, 2006; LaRue, Weiss, & Cable, 2008; Rowland & Schweigert, 1993; Spradlin & Siegel, 1982; Sundberg, 2008). Meaning defined by environmental context. The meaning of verbal behaviors is a function of their controlling variables (Hegde, 2008; Skinner, 1957). Speakers and listeners do not make mistakes, use the wrong word, or fail to generalize in the ordinary sense. …