Prelinguistic vocal development is "the process by which infants and toddlers produce increasingly more complex, phonetically diverse, and speech-like utterances before they say words on a regular basis" (Ertmer, 2005, p. 85). Research has shown that children with bilateral, moderate-to-profound hearing loss experience delays and deficits in vocal development compared with children who are developing typically. However, most of these investigations were completed before the widespread adoption of universal newborn hearing screening. More recent studies have shown that providing hearing aids or cochlear implants to infants and toddlers can lead to noticeable advancements in vocal development soon after sensory aid fitting. Given the increasing number of infants identified with hearing loss, there is a pressing need for a reliable and practical way to measure these auditory-based speech gains. This article describes the development and field testing of the Conditioned Assessment of Speech Production (CASP), a time-efficient tool for assessing children's progress in vocal development. CASP is based on 3 premises: (1) increased auditory access to conversational speech models and feedback through sensory aids will lead to noticeable advancements in vocal development; (2) sensory aid benefit is demonstrated when children imitate progressively more complex, phonetically varied, and speech-like vocalizations; and (3) toddlers can be conditioned to imitate developmentally appropriate speech stimuli modeled by a familiar person during a game-like activity. We conducted a field test with 13 children who had prelingual onset of hearing loss and 15 children who were developing typically. We explored 2 main questions: (1) At what ages will children actively participate in CASP? (2) Do CASP scores increase with age, sensory aid experience, and increased aided hearing levels? Field testing revealed that children as young as 12 months imitated CASP stimuli and that CASP scores increased with age and sensory aid experience. We did not detect a relationship with aided hearing levels. Implications for assessment and intervention are discussed.