In administering phonics inventories to his pupils, a teacher must be sure he is testing the pupils' knowledge of phonics ("sound sense") and not other or additional knowledge the pupils may possess. Administering this kind of extraneous-free test may be difficult in view of the great ranges of knowledge the students may bring to the testing situation. Therefore, it is the teacher's responsibility to employ in his phonics tests stimuli which he is relatively certain lie outside the ken of the respondents. It would seem, then, that using nonsense syllables (NSS: i.e. meaningless utterances) in phonics tests would be superior to using real words since the latter may be a part of the child's reading, listening or speaking vocabularies. For example, a pupil may not be able to identify the first phoneme in the NSS "moosh" but might be able to call by name that initial letter-sound in the word "mash" because he may have seen the television show or movie by the same name. Using "moosh," thus, may seem more reliable than using "mash" in testing the "m" sound.
Axelrod, J. (1976). Meaningful vs. Meaningless Utterances in Inventories and Their Effects on Pupil Performance. Reading Horizons, 16 (3). Retrieved from https://scholarworks.wmich.edu/reading_horizons/vol16/iss3/3