This study examines whether teachers' content adaptations to middle school math curricula align with mathematical learning progressions and explores their motivations for adaptation. This study originates from a concern that as teachers make adaptations to their lessons, they may make adaptations that move students away from the intended learning goal. Using a mixed-methods approach, we found that teachers were more likely to make productive over nonproductive adaptations. Teachers who made productive adaptations were more likely to consider learning progressions and adapt lessons to below-grade-level content. Teachers who made nonproductive adaptations were more likely to adapt lessons to on-grade-level content while delivering the lesson. Our findings suggest that districts should consider curricula and professional learning that intentionally highlight mathematical learning progressions.