To help explain the differences in students' performance on internationally administered science assessments, cross-national, video-based observational studies have been advocated, but none have yet been conducted at the elementary level for science. The USA and Germany are two countries with large formal education systems whose students underperform those from peers on internationally administered standardized science assessments. However, evidence from the 2011 Trends in International Mathematics and Science Exam assessment suggests fourth-grade students (9-10 year-olds) in the USA perform higher than those in Germany, despite more instructional time devoted to elementary science in Germany. The purpose of this study is to comparatively analyze fourth-grade classroom science in both countries to learn more about how teachers and students engage in scientific inquiry, particularly explanation-construction. Videorecordings of US and German science instruction (n[subscript 1]?=?42, n[subscript 2]?=?42) were sampled from existing datasets and analyzed both qualitatively and quantitatively. Despite German science lessons being, on average, twice as long as those in the USA, study findings highlight many similarities between elementary science in terms of scientific practices and features of scientific inquiry. However, they also illustrate crucial differences around the scientific practice of explanation-construction. While students in German classrooms were afforded more substantial opportunities to formulate evidence-based explanations, US classrooms were more strongly characterized by opportunities for students to actively compare and evaluate evidence-based explanations. These factors may begin to help account for observed differences in student achievement and merit further study grounded in international collaboration.