Educators have provided anecdotal evidence that systems-oriented instruction improves students' ability to comprehend complex systems, but little research has been done to test this hypothesis. This article reviews past attempts to assess systems-oriented instruction and suggests the need for an assessment tool that can be implemented broadly but still provides a nuanced view of individuals' understanding of complex systems. A tool called Cognitive Mapping Assessment of Systems Thinking (CMAST) is presented as a step toward addressing this need. Results from one study using this tool are included to illustrate analyses available and the significance of their results. Results from this study suggest that students receiving systems-oriented instruction exhibit significantly increased ability to understand information about a complex environmental system despite having received no specific training in natural resources. CMAST allows researchers to quickly obtain and evaluate quantitative data regarding students' ability to understand complex systems. Copyright © 2010 John Wiley & Sons, Ltd.