The paper discusses technology that can help students master four triangle centers -- circumcenter, incenter, orthocenter, and centroid. The technologies are a collection of web-based apps and dynamic geometry software. Through use of these technologies, multiple examples can be considered, which can lead students to generalizations about triangle centers.

### S. Asli Özgün-Koca and Matt Enlow

In this month's Growing Problem Solvers, we focused on supporting students' understanding of congruence and similarity through rigid motions and transformations. Initial understandings of congruence and similarity begin in first grade as students work with shapes in different perspectives and orientations and reflect on similarities and differences.

### Steve Ingrassia and Molly Rawding

Problems to Ponder provides 28 varied, classroom-ready mathematics problems that span grades PK-12, arranged in order of grade band. Links to the problem answers are available in this department.

### Mathew D. Felton-Koestler

Share news about happenings in the field of elementary school mathematics education, views on matters pertaining to teaching and learning mathematics in the early childhood or elementary school years, and reactions to previously published opinion pieces or articles. Find detailed department submission guidelines at http://www.nctm.org/WriteForTCM.

### Jenny Salls

Gain insight into students' understanding of the concept of fraction as operator as well as their reliance on rote procedures to convert fractions to decimals.

### Kelley Rudy

This department showcases students' in-depth thinking and work on previously published problems. The December 2012/January 2013 hands-on exploration of the history of chewing gum appeals to a wide range of learners. It was a perfect followup to a multiplication unit that a third-grade class in Pennsylvania had just studied.

### Kyle T. Schultz and Stephen F. Bismarck

A geometric approach using exact square manipulatives can promote an understanding of the algorithm to dismantle radical expressions.

A cartoon highlighting occupational uses of mathematics is coupled with a full-page activity sheet.

### Erin R. Moss

A good problem can capture students' curiosity and can serve many functions in the elementary school classroom: to introduce specific concepts the teacher can build on once students recognize the need for additional mathematics or to help students see where to apply already-learned concepts. We encourage teachers to use the monthly problem in their own classrooms and report solutions, strategies, reflections, and misconceptions to the journal audience.

### Signe E. Kastberg and R. Scott Frye

How do classroom behavioral expectations support the development of students' mathematical reasoning? A sixth-grade teacher and his students developed this example while discussing a ratio comparison problem.