The director general of secondary and higher education directorate professor Nehal Ahmed confirmed the matter on Wednesday.
Earlier, all primary schools were closed for four days -- between 5 June and 8 June -- to protect the children from the searing heat.
Meanwhile, on Wednesday, 26 students of three secondary schools at Daudkundi in Cumilla fell sick while attending the half-yearly examination.
Of them, 23 students were admitted to the Daudkandi upazila health complex for treatment.