Purpose: This report considered the validity of making conclusions about a child's phonetic inventory (the sounds a child can and cannot produce spontaneously without a prior model or other stimulation) based on the data from standardized single-word tests of articulation or phonology. Method: We evaluated the opportunities for production of word-initial consonants, word-final consonants, and vowels within the words included on 11 tests. Only words that met specific phonetic criteria (termed phonetically controlled words) were counted as opportunities for each consonant or vowel. Results: None of the tests provided sufficient coverage of consonants or vowels for establishing a phonetic inventory and making conclusions about the segments that a child can and cannot produce. Conclusion: Use of the data from a single standardized test of articulation or phonology would not be sufficient for completely inventorying a child's consonant and vowel production and selecting targets for therapy. It is recommended that clinicians supplement test data by probing production in additional phonetically controlled words.