A spot check by the Nation Sunday showed students from various schools buying books and uniform from shops in Nairobi.
Most of the schools are expected to reopen Monday and others Tuesday.
This comes amid a looming strike by teachers, which parents are opposed to.
Members of the Kenya National Union of Teachers (Knut) have threatened to start a job boycott in a week over the withdrawal of an annual salary increment and promotion by their employer.
The Teachers Service Commission scrapped the increment, arguing that the Collective Bargaining Agreement (CBA) with the teachers had addressed the issue.
Knut Secretary-General Wilson Sossion last week said all teachers have a right to an annual pay increment.
He said teachers will not perform their duties until the government meets their demands.
According to Mr Sossion, the increment is not a new demand but was in the 2017-2021 CBA.
University lectures have also threatened to go on strike on Wednesday over failure by the government to implement the 2013-2017 CBA.
Lectures’ strikes affected learning at the 33 public universities and their constituent colleges for a large part of this year.
During the January-April semester, students did not go for classes for two months due to a strike. During the May-August semester, the lecturers were on strike from July 3 to 18.
The third term is the most crucial in the school calendar, as Standard Eight and Form Four candidates sit their national exams.
The tests are expected to start in early October for secondary schools and late October for primary schools.
On Sunday, various parents who spoke to the Nation said the government should take measures to ensure teachers and lectures do not go on strike.
Mr Jones Nderitu, a parent, said the strike threats are causing panic among Standard Eight and Form Four candidates given the exams they are facing. “This is the time for teachers to closely monitor and guide students and prepare them for exams, but when they go on strike, it will adversely affect the children,” he said.
Another parent, Ms Mary Owino, said teachers should drop their plans to boycott work to allow candidates to write the national exams without disruptions.