According to various studies and the Cambridge University Student Barometer, Spanish students have the worst academic results in mathematics and English among the European Union countries. The objective of this study has been to analyze the influence of the teacher on motivation, positive emotions, metacognition strategies, and the academic performance of the students in those classes. We analyzed responses from 604 students of English and 547 students of mathematics, aged between 13 and 19 years. The teacher plays a relevant role in the motivation and emotions generated in the students, issues that determine decision making in the students’ learning and academic performance.