A deputy head teacher wrote to the Welsh government expressing concerns about behaviour at the school.
Dozens of children in one county have been sent to unaccredited online schools at a cost of more than £400,000.
Wales will be at an "economic disadvantage" if it doesn't increase student numbers, sector warns.
Parent Lisa from Hassocks says the changes should not apply to those already in private schools.
Parents will soon find out which schools their children will be attending from September this year.
Tilly Gerra requires support to study at university, but says she still faces "immense difficulties".
Pupil numbers are set to fall by 90,000 by 2040, but ministers want to maintain school staffing.
Staff were told they should note that higher marks are awarded at other universities.
Members of the EIS union were due to walk out on 20 February unless cuts were halted and reversed.
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