To equalize access to science learning across genders and demographic groups, access to the disciplinary language of science is one place to start. The language of science is highly challenging and specialized, and difficulties acquiring this language contribute to disparities in science achievement across diverse student groups. This study used a pre/post design to analyze effectiveness of a brief classroom science vocabulary assessment designed to assess receptive and productive vocabulary knowledge across multiple sections of one seventh-grade science teacher’s class. Vocabulary was selected and analysis conducted by an interdisciplinary research partnership, including the science teacher, a literacy specialist, and a scientist. The resulting model presents an assessment that evaluates receptive knowledge and productive use of science language and reinforces vocabulary theory: learning words is incremental and multidimensional, and assessment should address this specialized skill in principled, disciplined ways.