* After school for extra help or detention: The length of time a teacher can keep a student after school varies greatly by school district, state, and even individual school policies. Detention is typically limited to a short period (e.g., 30 minutes to an hour), while extra help sessions might be longer but are generally voluntary and should not be overly punitive. There are often specific rules and procedures for after-school detentions, requiring parental notification or consent in many jurisdictions.
* During the school day for disciplinary reasons: A teacher can temporarily hold a student in their classroom or a designated area for minor misbehavior, but this should be brief and only for the purpose of calming the student or addressing the issue. Extended isolation or confinement is generally not permitted.
* In a school-sponsored activity (e.g., field trip): The duration a teacher can keep students during a school-sponsored activity is determined by the planned schedule of the activity, and usually concludes when the activity ends.
* Illegal detention: Teachers are not legally allowed to detain students against their will beyond reasonable disciplinary measures. Unlawful imprisonment is a serious offense.
In short, a teacher's authority to keep a student ends when the school day ends or the planned activity is concluded, with the exception of reasonable and established disciplinary actions in accordance with school policy and possibly law. Any prolonged retention must be within the framework of established regulations and procedures. If you have concerns about a teacher keeping a student for an unreasonable length of time, you should contact the school administration.