The simplest of prekindergarten equations, 1 + 2 = 3, is the basis for an investigation involving much of high school mathematics, including triangular numbers, arithmetic sequences, and algebraic proofs.

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### Joshua David Jones

To be literate in a society where the information shared online is often exploited, learners should be exposed to multiple aspects of contemporary predictive modeling. Explore a lesson in which students learned an algorithm used in practice to automate the process of making recommendations.

### F. Paul Wonsavage

Three approaches to the Doughnut task highlight how representing functions in multiple ways can support student understanding in interpreting key features of functions within a context.

### Blake Peterson

Examining the covariation of triangle dimensions and area offers a geometric context that makes analyzing a piecewise function easier for students.

### Courtney Fox and Anna DeJarnette

This full unit in trigonometry introduces the world water crisis. Students engage in real-world problem-solving activities that access 21st-century skills while learning mathematics.

### Rebekah Elliott, Elyssa Stoddard, Megan Brunner, and Jenny White

The authors share a teacher-designed mathematical modeling routine geared to support teachers and to leverage opportunities for their students in learning important modeling practices and mathematical content.

### Michael S. Meagher, Michael Todd Edwards, and S. Asli Özgün-Koca

Using technology to explore a rich task, students must reconcile discrepancies between graphical and analytic solutions. Technological reasons for the discrepancies are discussed.

### Marina Goodman

Bridge the digital divide by teaching students a useful technological skill while enhancing mathematics instruction focused on real-life matrix applications.

### Amanda K. Riske, Catherine E. Cullicott, Amanda Mohammad Mirzaei, Amanda Jansen, and James Middleton

We introduce the Into Math Graph tool, which students use to graph how “into" mathematics they are over time. Using this tool can help teachers foster conversations with students and design experiences that focus on engagement from the student’s perspective.