Artificial intelligence (AI) is transforming many fields, including education. Can modern AI replace teachers? We discuss some popular AI applications for adaptive learning, how they are related to personalized education, what makes these applications "intelligent," and how the quality and quantity of student-generated data changes the behavior of adaptive learning systems and the learning experiences of students. If the data are scarce and corrupt, the benefits of adaptive learning are minimal. Motivated and persistent students generate greater amounts of high quality data and, as a result, tend to have better learning experiences. This can increase the gap between high achieving and low achieving students. More realistic student models and better understanding of the pedagogical context are needed to improve the performance of the AI educational systems. These are some of the reasons why experienced teachers cannot be replaced by the current AI applications.