Thinking about Interleaving

Of all the learning practices we have discussed in this forum, I think interleaving is one of the most counter-intuitive to students. So many of our "practice" structures are based around grouped or massed practice: lots of problems that emphasize one content area or one skill, and then a lot of problems addressing another content area or skill, and so on. I know I have tended to think about students' development of concepts and skills as a directional arrow, starting at "beginning" and ending at "more expert." So it is not too surprising that students have this idea as well.

One example from my non-work life helped me to appreciate the wisdom of interleaved practice. Two of my children used a middle-school mathematics curriculum that intentionally utilized interleaved practice: each problem set consisted of 15 questions that were relevant to that section of the chapter, with 15 additional questions that were taken from any of the previous sections or chapters. I saw first-hand the effect of this structure when my kids started recognizing that they had to go back to previous sections of the book to remind themselves about a kind of problem they hadn't seen for a while. Oh, the complaints! But I was amazed at the growth in my kids' ability to recognize different types of problems, to characterize them, and to explain how two seemingly unrelated math topics were actually very related. That is the strength of interleaving.

My kids' experiences in math, my reading about learning, and the encouragement of a departmental colleague prompted me to make some changes in my own teaching. I had been dismayed at the tendency of students not to make connections between different biology topics taught in the same class. The mental model I had was that they practiced and mastered one topic (for this example, some aspects of protein structure) but then "put away" that understanding after taking an exam on it, in the same way you might pack up holiday decorations after the holiday has passed. I realized that my actions were promoting this disconnect. 

So, I borrowed from the math model and redesigned my course. Each weekly quiz and each exam in my Introductory Biology course is now cumulative. For each assessment, I try to choose or design problems that promote connections between topics that might not seem related to a novice. I don't yet have a feeling about whether this has improved students' understanding of the material, but several of them told me they were not as intimidated by the looming cumulative final exam as they might have been, because they have been working with all the concepts and skills, all semester. In my experience, that alone is a win.