Carmel Martin, who has been one of U.S. Secretary of Education Arne Duncan’s right-hand people, will be leaving the U.S. Department of Education to oversee policy development at the Center for American Progress, a Washington think tank closely aligned with the Obama administration.

This is a potentially ground-shifting development at the Education Department. As assistant secretary for planning, evaluation, and policy development, Martin has overseen the creation of the department’s blueprint for revising the No Child Left Behind Act, and the waivers from the Elementary and Secondary Education Act. She’s also worked on many of the department’s marquee competitive-grant programs created under the American Recovery and Reinvestment Act, including the School Improvement Grant program.

And recently, when Duncan did a big sit-down with national reporters, Martin was the policy person he brought along. She’s played a role in a broad swath of the department’s policies.

Martin was well known inside the Beltway even before she went to work at the department. She was top aide to the late U.S. Sen. Edward M. Kennedy, a Democrat from Massachusetts, working on education issues. And she worked for two other Democratic former senators: Sen. Jeff Bingaman, of New Mexico, and Sen. Tom Daschle, of South Dakota.

Martin will be leaving in April. Denise Forte, who has been serving as deputy assistant secretary, will serve as acting assistant secretary (Martin’s role) until the job is filled permanently.