This is a PD opportunity presented by Colleen Lewis, Assistant Professor of computer science (CS) at the University of Illinois Urbana-Champaign.

"As novices, our students have trouble generalizing across coding problems to see the underlying structure. As a CS professor, I think that the most important code pattern students see is iteration. For example, consider Scratch code that plays 10 notes in a row or counts down from 100. Both of these use the iteration pattern, but their surface features might make students think that these two problems have nothing in common! I’ll share some varied instantiations of iteration in Scratch and try to convince you that helping students recognize this pattern can help them in their current and future CS learning. To show the connection to students’ later learning, I’ll share an example from my college classroom, where I show Scratch repeat blocks (that are nested and sequenced) to help my students reason about program efficiency (otherwise known as algorithmic analysis or Big-O)."