An idea to bring forward school summer holidays was a “non-starter”, a teaching union said.
The Welsh Government mooted the option as it considers how to reopen schools.
The National Education Union (NEU), said it would have meant a 20-week autumn term but the Conservatives have expressed disappointment.
A government source said it was “a sensible and workable option” but “recognised and respected” unions were not in favour.
The proposal would have seen the six-week summer holiday begin near the end of June, with the new school year beginning early August.
BBC Wales has been told the rationale included:
- Good weather lets schools maximise use of outdoor space
- The virus is thought less transmittable in sunlight and outdoors
- August schooling could give pupils more time in school before a potential second peak in autumn or winter.
Plaid Cymru said the idea should be “explored further.”
The Brexit Party said “union diktat” was stopping pupils returning to school.
On BBC Radio Wales, NEU Cymru secretary, David Evans, said: “It would mean there would be a 20-week term in the autumn with just a one-week break in the middle for the teachers.”
He said it would mean breaking summer arrangements and there would be “contractual issues”.
“By the time you put all that together the complicating factors just mean it’s a non-starter,”Mr Evans said.
In England, some pupils will return on Monday.
In Scotland, where the summer holiday is earlier, pupils will return on 11 August.
Suzy Davies MS, Conservative education spokeswoman, said: “The two main considerations here are that teachers don’t lose a second of their much-needed summer break and that pupils’ time away from school doesn’t last a second longer than necessary.
“The solution also has to take into account the practicalities of councils having to find transport and other support for schools opening in a phased approach.
“I’m disappointed that the door appears to have closed so firmly on bringing a full summer holiday period forward by even a week. I am speaking to the unions this week anyway and look forward to hearing their reasoning.”
Plaid Cymru education spokeswoman Sian Gwenllian MS, said bringing the holidays forward should continue to be examined.
“A phased and gradual re-opening of schools could then start in August, if it is safe to do so,” she said.
Brexit Party Senedd leader, Mark Reckless, said: “The desire of parents and pupils to get back to school is ignored due to union diktat.
“Starting the autumn term in early August would minimise disruption to kids’ learning.”
The Welsh Government said it was working with unions, councils, scientists and head teachers.
“The minister intends to update further next week,” a spokesman said.