States and districts across the country are grappling with how to incorporate assessments of student learning into their teacher evaluation systems. Sophisticated statistical models have been proposed to estimate the relative value individual teachers add to their students' assessment performance (hence the term teacher "value-added" measures). The strengths and limitations of these statistical models, as well as the value-added measures they produce, have been widely debated. Little attention, however, has been devoted to the quality of the student assessments that these models use to estimate student growth, which is fundamental to the trustworthiness of any teacher value-added measure. Assessments that nominally address the subject or grade level that educators teach do not necessarily suffice for the purposes of measuring growth and calculating the value that teachers contribute to that growth. In fact, student growth scores require at least two assessments of student learning--one near the beginning of the school year or the end of the prior year and another at the end of the current school year. Carefully designed and validated assessments are needed to provide trustworthy evidence of teacher quality. Herein lies the purpose of this brief: to provide guidance to states and districts as they develop and/or select and refine assessments of student growth so that the assessments can well serve teacher evaluation purposes. This brief identifies an extensive set of propositions, claims, and evidence sources that are important to the validity argument and which justify the use of student growth assessments as part of teacher evaluation. (Contains 1 footnote, 1 figure, and 1 table.) [For the extended version of this document, "Guidance for Developing and Selecting Assessments of Student Growth for Use in Teacher Evaluation Systems (Extended Version)", see ED524088.]