Teacher feedback in mathematics is a potential strategy for redressing declining international trends in high school mathematics achievement. Effective feedback comprises corrective information (feedback) and guidance for improvement (feedforward)--referred to herein as 'feedback-feedforward'. Relatively little research has examined the motivational mechanisms linking teacher feedback to achievement, with even less linking feedback-feedforward to achievement. Goal setting theory proposes that goal setting, especially growth-oriented (e.g. personal best) goal setting, may mediate the positive impact of feedback on achievement. Using structural equation modelling, this study (N = 362 Australian students) builds on this to examine if: (1) teacher feedback-feedforward and PB goal setting predicted achievement in mathematics; and (2) PB goal setting mediated the link between teacher feedback-feedforward and achievement. Mathematics teacher feedback-feedforward predicted PB goal setting, PB goal setting predicted achievement, and PB goal setting fully mediated the link between feedback-feedforward and achievement. Implications for mathematics teacher feedback-feedforward and goal-setting interventions are discussed.