Stephen Mccabe, the joint chair of the Education Recovery Group at the Scottish government, said there were "serious concerns" among teaching unions about the safety of their members returning to work.
He warned that unions wanted safety concerns dealt with before they would support the reopening of schools, including clarity over personal protective equipment (PPE) stock levels, as well as cleaning rotas.
"There are a number of unresolved issues," he said, "The unions want to know about access to PPE for staff and whether there are enough resources available for appropriate cleaning in schools.
“They want to know what surveillance testing there will be in schools, particularly for staff and for senior pupils who appear to be at higher risk than younger children, and there remain issues around public transport and what measures should be taken to protect pupils.
"It is absolutely not a done deal that Scottish schools will go back full-time on August 11 despite the positive trajectory we are on."
McCabe said "a great deal of nervousness" remains in government over easing of the lockdown. This weekend, the biggest daily rise in new confirmed cases of Covid-19 in almost a month was confirmed as Nicola Sturgeon, the first minister, urged the public to be vigilant as pubs and restaurants allow patrons indoors.
Yesterday the Scottish government confirmed there had been a further 21 new positive cases of coronavirus - the highest rise in the infection figures since June 21 - and a significant increase on the three new cases reported on Tuesday.
Deputy first minister John Swinney warned the public of the ongoing threat of coronavirus, with the surge in positive cases coming after lockdown measures were eased on Wednesday.
He tweeted: "Thankfully another day of no deaths recorded due to #COVID. 21 positive cases however remind us of the danger still out there."
The data also shows there were no deaths involving someone who had been confirmed as having Covid-19, meaning the death toll under this measurement remains unchanged from Thursday at 2,491.
A total of 18,422 people have now tested positive for the virus in Scotland.
This story originally appeared in the Sunday Times.
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