Although teachers are expected to teach mathematics ambitiously, it is challenging for them to do so. Given that the first year represents a critical juncture between teacher preparation and inservice teaching, it may be particularly challenging to teach ambitiously. Understanding the nuanced characteristics in lessons taught by first-year elementary teachers identified as being generally ambitious can inform how mathematics teacher educators and school mentors support them. A thematic analysis of 15 transcribed lessons revealed instructional moves that were more and less prevalent. Task-level findings indicated that while first-year teachers solicited student input, encouraged them to participate in discussions, and had them attend to cognitively demanding tasks, they seldom assigned open-ended and non-procedural tasks. Students also had few opportunities to grapple with the mathematics. Turn-level findings indicated that first-year teachers maintained the task potential, facilitated student participation, and promoted student authority and perspectives. They further aimed to deepen students' mathematical thinking, albeit the subtle ways they did so sometimes were apparent across lessons (e.g., encourage students to continue to problem solve) and other times were limited (e.g., provide an opportunity for students to agree or disagree).