The 12-key approach is considered a foundational practice strategy for jazz instrumentalists. Its relevance to vocalists, however, seems less clear. This article investigates improvising jazz vocalists' perceptions and experiences of using the 12-key approach as distinguished from instrumentalists'. It uses data from a two-phase, mixed methods study. Phase one of the study utilised an anonymous, online survey to investigate vocalists' and instrumentalists' perceptions and experiences of jazz education and performance. The second phase utilised interviews with skilled Australian jazz vocal improvisers and with senior jazz educators in Australian tertiary institutions. The combined results reveal that vocalists predominantly regard the 12-key approach as less helpful to their work as jazz musicians than do instrumentalists. The difference was commonly attributed to a difference in the motor programming needs of the two groups. Physical limitations of performing in 12 keys were also repeatedly cited as interfering with the method for vocalists. Two interviewees connected the repetition of 12-key practice as beneficial in developing procedural knowledge useful for improvising. Such possible cognitive benefits suggest that the method should be further investigated before decisions are made on its value to vocal jazz improvisation education.