It's 10 a.m. on a Wednesday at Paterson (NJ) School Number 2, and seven teachers are crowded around a circle of student desks, debating how to introduce the concept of geometric shapes to a special education class. Brightly colored foam shapes are piled on one desk, while rectangular perfume boxes and cylindrical tennis ball containers clutter another.

"We can start the lesson by asking them to group similar objects together," suggests 5th-grade teacher Beatrice Parga.

"I'm concerned these kids will characterize the shapes by color instead," says 8th-grade teacher Bobbie Wolff, "or maybe group all the pointy things together—like cones and triangles."

"Maybe it would be good if they group them in a way we don't want them to," says Bill Jackson, the school's math coordinator. "They may learn that three out of the four shapes have parallel, congruent faces."

The teachers trade and debate ideas as they try to anticipate how students will respond to the lesson and what teachers can do to turn those responses into learning opportunities. They are engaged in lesson study, a professional development process developed in Japan.