Virtually nothing is known about the role that tone of voice may play in motivating interactions. Herein, we use an experimental approach to explore for the first time how the same directive instructions ("Do well at the play") have different effects on adolescents depending on the motivational tone of voice used to convey these instructions. A sample of 1,000 adolescents aged 14-15 years was randomly assigned to hearing semantically identical messages that were expressed by mothers of adolescents with controlling, autonomy-supportive, or neutral tones of voice. Results suggest that the way speakers modulated their voice when intoning the same verbal messages affected adolescents' emotional, relational, and behavioral intention responses. Listening to mothers making motivating statements in an autonomy-supportive, relative to a neutral, tone of voice elicited more positive and less negative emotions, increased closeness, and intentional behavioral engagement among adolescents, while the opposite set of findings emerged when adolescents listened to mothers making motivational statements in a controlling tone of voice. These findings elucidate how mothers' spoken communications can impact adolescents, with implications for the quality of parent-child relationships, adolescents' well-being, and engagement.