The arrival of the Next Generation Science Standards (NGSS) marks a new era in science education. However, like all education reform, the success of NGSS implementation lies with teachers. Effective and targeted professional development will play a key role in preparing teachers who work from the framework. This study sought to design and validate a survey instrument measuring elementary teachers' perceived understanding of the NGSS framework. After developing and modifying the initial item pool through expert review and piloting, the instrument was administered to 167 elementary teachers from Montana, Utah, Idaho, and Wyoming. Results from an exploratory principal components analysis yielded a five-factor model which explained 74% of the variance. Through Confirmatory Factor Analysis, the five-factor model was found to be an acceptable fit to the hypothesized population model. The 31-item instrument holds promise as a tool for informing professional development efforts related to teachers' understanding of NGSS concepts. It could be used as part of a needs assessment when planning for professional development. Whether part of a needs assessment or a smaller scale effort, the instrument could be used to identify areas for targeted growth in understanding of NGSS concepts.