An assessment-related stress is an object of interest of both educational and neurobiological research. In educational literature, “feeling stressed” is measured by self-reports and mostly in the situation of high-stakes examinations before and after an exam. In neurophysiological research, “acute stress” is laboratory observed through controlled variables. However, the studies of functionally measured stress in real school context are missing in scientific literature. This article relates the results of a study carried out in a real school context during a class test. Stress data obtained through the functional measurement (heart rate variability) in 16 students and behavioral data in 76 students were analyzed. The results show that class tests under assessment are more stressful compared with nonassessed tests. A decrease in number of correct responses and an increase in response time was observed. Girls show better performance and respond more slowly under assessment. The results are discussed in the scope of interdisciplinary research.