Compound interest is one of the most important topics in financial mathematics and one of the least learned school content, along with combinatorial and statistical analysis.
The reason is obvious: the material placed (and the way it is placed) seems very distant from the students' reality. And the rule is always valid: the more abstract a theme, the lower its degree of retention.
Nevertheless, after adults, the importance of knowing how to calculate compound interest is present in everyday life, when you want to make a payroll loan, predict how much your savings will be or even understand a vehicle or real estate financing simulator. In other words, of mathematical abstractions, it is one that has more application in people's lives.
Without the notion of the behavior of money over time, the person ends up mentally equalizing different quantities, such as money today and money tomorrow (without taking into account monetary correction and opportunity cost).