The significance of inquiry skills is widely acknowledged in science practice across many areas. Carrying out experimental investigations is an indispensable element of scientific inquiry and, therefore, an important capability to assess. Drawing on research development in assessment design, this report provides a design pattern to help assessment designers create tasks assessing students' reasoning skills in experimental investigation, The design pattern lays out considerations regarding targeted knowledge and skills in this inquiry process, characteristics of situations in which students can evidence that skill, and ways of evaluating their work with specific examples.