The decision follows investigations that revealed cases of collusion, use of unauthorized materials, and mobile phone violations.
The 2025 KCSE exams ran from October 21 to November 21, with oral and practical assessments preceding the written papers.
The national assessment cycle included over 3.4 million learners across KCSE, KPSEA, and the inaugural KJSEA.
A total of 996,226 candidates registered for the KCSE, comprising 492,012 male and 501,214 female candidates.
The irregularities, KNEC said, contravened exam regulations, necessitating strict disciplinary action to uphold exam integrity.
KNEC also released a list of schools involved in the infractions.
Western Kenya recorded the highest number of cases, with Bungoma leading at 56 incidents, followed by Kakamega (50), Vihiga (10), and Busia (2).
The violations included collusion, unauthorized materials, and mobile phone use during exams.
In some schools, multiple candidates were implicated in a single irregularity, prompting mass result cancellations in affected centers.
In Kakamega, St Stephens Lwanda reported 33 candidates involved in collusion in Chemistry, while Butere Girls had six students caught with unauthorized materials in Mathematics.
Dr. David Lewis Heritage School had four students using prohibited aids.
Bungoma schools dominated the list, with Mitua Girls recording over 20 students caught with unauthorized Kiswahili materials.
Chesamisi and Teremi Boys were flagged for mobile phone use, while Kirane High reported collusion among three candidates.
Vihiga schools were also affected. Stanley Godia Secondary and Goibe Girls had multiple candidates using unauthorized Biology, Mathematics, and English materials.
Chavakali High, Mbale High, and Kaimosi Boys reported isolated unauthorized material cases.
KNEC reiterated its commitment to integrity in national examinations and warned schools and candidates against further violations.
The council urged all stakeholders to follow exam regulations strictly to avoid sanctions.
The council also advised parents and guardians to educate learners on ethical exam practices.
KNEC emphasized that such measures safeguard the value of certificates and protect candidates’ future academic and professional opportunities.
The full list of affected schools and candidates is available on KNEC’s official website.
Investigations into other suspected irregularities are ongoing, as the council seeks to maintain public confidence in Kenya’s national assessment system.
