This manuscript details our efforts to assess and compare students' learning about electricity in three countries. As our world is increasingly driven by technological advancements, the education of future citizens in science becomes one important resource for economic productivity. Not surprisingly international large-scale assessments are viewed as significant sources of information about the effectiveness of science education. However, these assessments do not provide information about the reasons for particular effectiveness--or more importantly a lack thereof--as these assessments are based on one-time measurements of student achievement. In order to identify reasons for the effectiveness of science education, it is necessary to investigate students' learning as a result of science instruction. In this manuscript we report about the development of an instrument to assess students' learning in the field of electricity and the use of this instrument to collect data from N?=?2,193 middle school students in Finland, Germany and Switzerland prior to and after instruction on the topic of electricity. Our findings indicate that the differences in students' science achievement as observed in large-scale assessments are a result of differences in students' science learning. And our findings suggest that these differences are more likely to stem from differences in science instruction than from systemic differences: a result that needs to be further explored by analyzing instruction in the three countries and its effect on students' learning.