In the push to boost young people's social and emotional learning (SEL), assessment has lagged behind policy and practice. We have few usable, feasible, and scalable tools to assess children's SEL. And without good assessments, teachers, administrators, parents, and policymakers can't get the data they need to make informed decisions about SEL. Some existing SEL assessments, writes Clark McKown, are appropriate for some purposes, such as keeping teachers abreast of their students' progress or evaluating SEL interventions. But too few high-quality SEL assessments are able to serve a growing range of purposes--from formative assessment to accountability, and from prekindergarten through high school. McKown recommends proceeding along two paths. First, he writes, educators should become familiar with existing SEL assessments so that they can learn their appropriate uses and limits in a low-stakes context. At the same, we need to invest money and talent to create assessment systems that can be used to meet important assessment goals at all grade levels. McKown walks us through definitions of SEL, identifying three broad areas of SEL skills-- thinking, behavior, and self-control. Each area encompasses skills that are associated with important life and academic outcomes, that are feasible to assess, and that can be influenced by children's experiences. Such meaningful, measurable, and malleable skills, McKown argues, should form the basis of SEL assessments. The next generation of SEL assessments should follow six principles, he concludes. First, assessments should meet the highest ethical and scientific standards. Second, developers should design SEL assessment systems specifically for educational use. Third, assessments should measure dimensions of SEL that span the three categories of thinking, behavioral, and self-control skills. Fourth, assessment methods should be matched to what's being measured. Fifth, assessments should be developmentally appropriate--in other words, children of different ages will need different sorts of assessments. Last, to discourage inappropriate uses, developers should clearly specify the intended purpose of any SEL assessment system, beginning from the design stage.