A teaching union claims that some Jersey pupils are being told to bring blankets to school and some teachers are leading lessons in hats and coats because classrooms are so cold.
The NASUWT says that's because risk assessments advise that all windows and doors are kept open to reduce Covid spread.
The union has called the decision to open schools 'untenable' and has accused the government of failing to meet its responsibilities to keep staff and pupils safe.
Keeping Jersey schools open is untenable https://t.co/iQW4e1cSWA— NASUWT (@NASUWT) January 12, 2021
It wants students to work from home, and for more safety measures to be introduced for the children of keyworkers who would need to go to school.
Examples given include wearing face coverings in all indoor areas, stringent social distancing and allowing vulnerable staff to work from home.
NASUWT General Secretary Patrick Roach says pupils and staff are being made to soldier on in conditions which are anti-ethical to high-quality teaching and learning, which -he says 0 is putting their health and safety at unnecessary risk.
"The NASUWT has been pressing hard for additional mitigations to be put in place for schools but these calls have been ignored by the Government.
"A move to remote learning now would help to safeguard the health and welfare of children, young people, school staff and the wider community and is the only sensible course of action in the current circumstances.
"Ministers cannot continue to stubbornly disregard the welfare of pupils and the education workforce and must act to keep everyone safe and supress the virus."
Senator Tracey Vallois resigned as Education Minister on Sunday 10 January after disagreeing with the decision to reopen schools - citing concerns from families, uncertainty over the presence of a new variant of Covid-19 in Jersey, and claims she views were repeatedly dismissed.
The government reopened schools after extending the Christmas holidays by an extra week to give staff more time to prepare for a safe return to the classroom and to introduce a voluntary testing regime for teachers and Year 11, 12, and 13 students.
1,912 school staff (of whom 1,351 were teachers) were tested during the first ten days of January. Four tested positive.
Out of 1,510 15 to 18 year olds who were tested, the government says 'fewer than 5' tested positive.
6% of Jersey students were marked as having unauthorised absence from school on Monday 11 January, the first day back this term.
7.2% of absences were Covid-related.
93.6% of primary school students attended, along with 83% of secondary pupils.
The Children's Commissioner welcomed the return to school, but called for a unified message of support from politicians and work to make sure all students working from home have the necessary equipment.
Acting Education Minister Deputy Jeremy Macon, who will be in temporary charge until a replacement for Senator Vallois is finalised, called the return 'safe and successful' and gave a reason for the lower attendance at secondary schools.
"I am pleased to publish the latest student attendance figures. These show we have had an encouraging start of term for primary students returning to schools yesterday following an extended Christmas school holiday break.
"The secondary school figures are lower, but in part due to one year group off school due to staff shortages and a number of Covid-19-related absences. We will continue to work with schools to support them and monitor the situation daily with the Department.
"I am pleased to also publish the latest PCR testing figures for nursery, school and college staff and secondary school students in years 11-13. I would like to thank all those who have taken part in this voluntary testing programme. Out of almost 3,000 tests there have been very few confirmed cases which is very encouraging."
Channel 103 has contacted the government for a response to the NASUWT's criticism. We await a response.