Police say the incident occurred on Thursday during a Christian Union session within the school compound, a gathering that had been expected to proceed peacefully before the confrontation unfolded.
According to area Police Commander Mohammed Godana, the suspect, a 23-year-old day scholar at the same institution, confronted the victim during the session before allegedly attacking her.
He is said to have stabbed her in the chest and left arm before being restrained and taken into custody following the incident.
Authorities have not yet established the full circumstances that led to the confrontation, but preliminary reports suggest the two students may have been involved in a personal dispute believed to be linked to a romantic relationship.
Investigations are ongoing to determine the events leading up to the attack and whether other students were involved or witnessed the incident.
The victim was quickly rushed to AIC Litein Mission Hospital, where she is currently admitted and undergoing treatment.
Medical officials have not released further details on her condition, but sources indicate she remains in serious condition and under close observation.
Security officers visited the school shortly after the incident to secure the scene and begin initial investigations.
Police have also been interviewing students and staff present during the Christian Union meeting in an effort to piece together what transpired before the attack.
Commander Godana confirmed the arrest of the suspect, who is being held in custody as detectives continue with inquiries.
He added that appropriate legal action will follow once investigations are complete and the file is forwarded to the Director of Public Prosecutions.
The incident has raised concern among parents and education stakeholders in the region, with calls for stronger measures to address discipline and interpersonal conflicts among students in learning institutions.
Some residents have also expressed concern over the presence of an over-age learner in a secondary school environment, urging authorities to review admission and monitoring processes.
Education officials are expected to visit the school to assess the situation and provide guidance on counselling and support services for students affected by the incident.
Teachers have also been urged to maintain calm as normal learning activities resume under heightened attention.