Barriers to effective provider-patient communication take many forms that can be difficult to recognize and appropriately address. This paper offers probabilistic indicators for one such form, patient-produced "I don't know" (IDK), distinguishing its use as a cognitive claim and its use as a strategy for resisting discussion of sensitive topics. A total of 95 audio-recorded psychiatrist-child interactions are drawn from a US-wide corpus of physician-patient consultations. From these, 376 patient-produced IDKs are extracted and coded for linguistic/social factors, including form, function, prosody, age, gender, and primary diagnosis. Two multiple logistic regressions are performed to determine the predictors of cognitive and resistive IDK functions respectively. Cognitive IDK uses are associated with the full form (p < 0.01) and unstressed prosody (p < 0.01). Use of resistive IDK is correlated with decreasing patient age (p < 0.01) and emotionally labile mental health diagnoses (p < 0.01). Cognitive and resistive IDK uses have distinctive linguistic and social distributions in psychiatrist-child interactions, where cognitive uses have two objectively identifiable linguistic characteristics and resistive uses are associated with certain patient types. Providers may learn to recognize cognitive and resistive IDK uses, thus acquiring the ability to correctly interpret interactional cues relevant to the diagnosis and treatment of pediatric mental health conditions.