The primary purpose of this study was to investigate the effects of a singing-aural imitation treatment on collegiate instrumentalists' jazz performance achievement and self-efficacy to play and teach jazz and improvisation. A secondary purpose was to investigate to what extent various background variables might relate to jazz improvisation achievement. Participants (N = 18) in the study received approximately sixty-minutes of jazz instruction. Jazz performances were evaluated by three expert judges using the researcher-constructed Jazz Melody and Improvisation Performance Achievement Measure. Results indicated significant increases from pre- to posttest on participants' ability to sing the notated jazz melody, nearly significant increases in participants' jazz improvisation, and non-significant differences in participants' ability to play the notated jazz melody. Participants reported greater self-efficacy for jazz performance and jazz teaching at posttest compared to pretest. The number of years participants spent in a jazz ensemble and improvising in genres other than jazz significantly correlated with scores on some of the performance measures. Findings of this study associated with singing strongly suggest that music educators should incorporate singing (a systematic vocalization system) in their instruction.