As many as 936 classes at primaries and 495 classes at secondary schools were quarantining on Tuesday, the total number being three times that of the figure before Christmas holidays.
A total of 19,651 primary pupils and 12,808 secondary students were isolating on Tuesday.
Only at primaries 1,068 infections were confirmed in pupils and an additional 406 in staff. At secondary schools, where the vaccination rate is higher, 379 infections were confirmed among students and 84 among staff.
At kindergartens, 171 classes numbering a total of 2,446 kids were isolating. On Tuesday, 74 infections were confirmed in kindergarten children and 235 in kindergarten staff.
Before Christmas holidays, as of 23 December, 372 primary and 52 secondary school classes were quarantined.
Gregor Pečan, the head of the Headteachers of Primary and Music Schools, said the situation was getting critical, suggesting for winter holidays to be moved forward to coincide with the peak of the 5th wave.
Pečan's school saw three teachers sent into quarantine only on Tuesday. "If that happens in two more classes, we can shut down years 5 to 9 because there will be no staff to give lessons," he told the STA.
He says the main problem is the new rule under which the teacher is ordered to self-isolate if they were in the same classroom with an infected pupil for 15 minutes, up from the previous rule of 45 minutes.
Since epidemiologists expect the 5th wave of infections to culminate in two weeks, Pečan suggested considering moving winter school holidays from the end of February to the end of January.
Radio Slovenija has reported the Ljubljana Secondary School for Pharmacy shifted fully to remote classes on Monday and the Ljubljana Secondary School of Economics is moving online on Thursday.
Nives Počkar, the head of the Association of Secondary School Teachers, also told the radio further schools would have to be closed due to infections and quarantine orders.
Slovenia reported a record 7,420 coronavirus infections for Tuesday.