Seventy six registered candidates from South Sudan did not write KCSE tests in Turkana on Monday due to insecurity concerns.
County education director Pius Ong'oma noted tension after killings at Lokichogio Mixed Secondary School caused the students from the neighbouring country not to turn up.
"The heightened security along the borders has forced candidates not to cross the borders. We communicated over phone and made them aware of exams but they did not turn up."
Suspected Toposa militia raided the school on October 14, killed six students and a watchman and injured 18 other people.
Survivors said the fight resulted from a dispute over the purchase of a lotion.
A mob dragged suspect Abraham Lojore, a student from South Sudan, from Kakuma police station and killed him.
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Ong'oma added examinations were delayed in some parts of Turkana due to heavy rainfall.
"We were forced to use a helicopter to dispatch materials to impassable regions," he said.
"In Turkana central, the flooding of seasonal river Kawalase hindered the start of exams as transport was disrupted."
Turkana has a total of 3,816 registered KCSE candidates.