Is it illegal for teachers to keep students after the bell rings in the US?

In the U.S., whether it's illegal for teachers to keep students after the bell rings depends on school policies and state laws rather than a specific federal law. Generally, teachers can request students to stay for educational reasons, but they must ensure that students are safe and supervised. If a student feels uncomfortable or is kept excessively, it might raise concerns regarding student rights or school regulations. Parents and students should consult school handbooks or administration for specific policies.