School anxiety is defined as a set of symptoms grouped into cognitive, psychophysiological and motor responses emitted by an individual in school situations that are perceived as threatening and/or dangerous. This study analyzed the relationship between school anxiety and academic achievement in a sample of 520 Spanish students (40.8% boys) from 12 to 18 years. School anxiety was measured with the School Anxiety Inventory (SAQ). The SAQ measures seven factors: four school situations (Anxiety faced with School Failure and Punishment, Anxiety faced with Aggression, Anxiety faced with Social Evaluation, and Anxiety faced with School Evaluation), and three anxiety response systems (cognitive, physiological, and behaviour). Academic performance was measured by scores on the subjects of language and mathematics. Also, we recorded the number of failed subjects of each student. Results revealed that students with high performance in language had significantly higher scores in anxiety faced with school failure and punishment, anxiety faced with aggression, behavioral anxiety and psychophysiological anxiety than their peers with low performance in this subject. Similarly, students with high academic performance in mathematics had significantly higher scores in anxiety faced with school failure and punishment, anxiety faced with aggression and behavioral anxiety than their peers with low performance in this subject. Therefore, non-clinical anxiety in certain situations school improves academic performance. Overall, these results support those found in previous research, which indicate a higher academic performance of students with certain fears school. Results of this study are important because they provide a more comprehensive analysis of the relationship between school anxiety and academic achievement. In this regard, this study reveals the importance of taking into account school anxiety as a multidimensional construct.