This article discusses how a school librarian can help students improve their critical thinking and strengthen their higher order thinking skills through the inquiry process. First, it will use a Guided Inquiry approach to examine how higher order thinking skills are taught within an inquiry paradigm. Next, it will consider how formative assessments can be used to match the teaching to the student's learning needs during inquiry. Finally, it will look at a critical-thinking checklist, a formative assessment tool to help teachers focus on specific learning targets of critical thinking during observations. A post-observation worksheet follows to help analyze the observational notes to create meaningful next steps for instruction. (Contains 7 figures.)