Since 2011, Illustrative Mathematics (IM)—which has reached over three million students and educators—has been guided by the vision, expertise, and heart of our CEO and cofounder, Bill McCallum. Today, we are announcing a milestone for IM: At the end of this month, Bill will transition from his role as CEO to a new position as senior advisor. As we begin this next chapter in IM’s journey, we want to celebrate everything Bill has made possible as the chief executive officer of IM and one of the most prominent and influential leaders in K–12 mathematics education in the United States.
From the very beginning, Bill’s belief has been clear and unwavering: Mathematics belongs to everyone, and all learners deserve to know, use, and enjoy it. This belief became the shared vision of Illustrative Mathematics, and it remains the heartbeat of everything IM does today.
From Academic to Advocate for Access
Before cofounding IM, Bill had already made a name for himself in both the world of mathematics and mathematics education. As a research mathematician and distinguished professor of mathematics at the University of Arizona, and one of the lead writers of the Common Core State Standards for Mathematics, he had a unique ability to connect big ideas in mathematics with what actually happens in classrooms—and the credibility to bring many constituencies together to support his vision.
Bill teaching at the University of Arizona, June 2004
Bill didn’t just want to write standards—he wanted to bring them to life. He wanted to build tools that would help teachers bring high-quality, meaningful math instruction into every classroom. This passion led to the creation of Illustrative Mathematics, which began as free mathematics tasks to illustrate the standards—hence the name. It later evolved into a nonprofit that now serves millions of students and educators nationwide.
Building IM from the Ground Up
Bill’s leadership style has always been collaborative, thoughtful, and deeply principled. He believed in building something with teachers, not just for them. That ethos is embedded in IM’s DNA. Under his leadership, IM’s dedicated team of mathematicians and educators designed a problem-based math curriculum that prioritizes classroom discourse, balances conceptual understanding, procedural fluency, and application, and fosters joy in learning.
As IM’s CEO, Bill has championed the idea that students learn math by doing math. He has ensured the curriculum invites students into meaningful problem-solving, productive struggle, and real mathematical thinking, while honoring the teacher’s role as a true professional. He helped shift the narrative from an either-or view of understanding concepts versus learning procedures to a vision of math as a sense-making journey, where both develop in tandem—a shift that continues to inspire classrooms using IM Certified® curricula across the country.
Bill with teachers at Green Charter School in New Orleans during an IM school visit, January 2021.
A Leader with Heart
Ask anyone who’s worked closely with Bill, and they’ll tell you he leads not with ego, but with empathy and humility. He listens deeply. He asks the right questions. And he never loses sight of the mission: to ensure that all students have access to high-quality math instruction.
Even as IM grew from a university-based project into a nationally recognized nonprofit, Bill stayed grounded in the work of teachers and students. He never stopped thinking about the classroom. He never stopped learning. And he never stopped reminding all of us that every student deserves to see themselves as a mathematician.
Passing the Torch
With the same thoughtfulness that has guided his entire career, Bill is now passing the torch to his longtime colleague and fellow cofounder, Kristin Umland, who will step into the role of CEO on August 1, 2025. Kristin brings her own powerful vision and deep expertise in math education to the next chapter of IM’s journey.
Bill and Kristin have worked side by side for years, helping to shape IM’s unique voice and approach. Their collaboration has been instrumental in building a culture that values coherence, community, and teacher partnership. In many ways, this transition is not a departure but a continuation of the vision they began building together more than a decade ago.
Bill and Kristin at the 2024 IM Employee Retreat
Looking Ahead with Gratitude
While Bill may be stepping back from day-to-day operations, his influence remains ever-present at IM. As senior advisor, he will continue supporting IM’s mission and leadership, offering wisdom and guidance as the organization grows and evolves.
This is not goodbye. It’s a well-deserved celebration of a remarkable leader whose work has touched millions of lives—and a moment to look ahead to what’s next.
To Bill: Thank you for your vision. Thank you for your heart. And thank you for reminding us—always—that all learners can know, use, and enjoy mathematics.
Here’s to the next chapter.
With deepest gratitude,
The IM team
Bill by the Numbers
Here’s a quick look at Bill’s journey through the lens of some remarkable milestones:
Each of these numbers tells a story—not just of Bill’s incredible contributions to the field, but of the lasting influence he’s had on students, teachers, colleagues, and classrooms across the country.
Have a favorite memory or message for Bill?
Add your note to this virtual card and join us in celebrating the impact he’s had on so many educators and students.
Click here to sign the virtual card.
