Curriculum top study (CTS) action research is a specific type of inquiry that combines curriculum topic study (Keeley 2005) with an examination of students’ thinking using formative assessment probes (Keeley, Eberle, and Farrin 2005; Keeley, Eberle, and Tugel 2007; Keeley, Eberle, and Dorsey 2008; Keeley and Tugel 2009) and a variety of data-collection techniques designed to reveal alternative ideas students have about science concepts. This article describes how to combine CTS with formative assessment probes to create a revealing form of action research.