However, shadow education secretary Kate Green said other measures including mask-wearing, ventilation systems and testing were also needed.
On Friday, vaccine experts did not recommend the jab for healthy 12 to 15-year-olds on health grounds alone.
But the UK’s chief medical officers have been asked to consider any wider implications of extending the rollout.
The government believes there is a “strong case” for offering the vaccine to healthy 12 to 15-year-olds to reduce disruption in schools and keep infection rates down as winter approaches, a source has told the BBC.
A final decision is expected within days.
Ms Green said as soon as the chief medical officers gave their advice, “the government needs to take a clear decision”.
“It’s very disappointing that we have had to wait so long to reach this point where there will be clarity,” she told BBC Radio 4’s PM programme.
“But once we have a decision, if it’s to go ahead, that needs to be clearly communicated and there needs to be a process in place to deliver those vaccinations.”
However, she said vaccinations alone would not be enough to prevent disruption in schools.
The shadow education secretary also called for mask-wearing, improved ventilation and a robust testing system to reduce the spread of Covid and keep children in classrooms.
Face coverings are no longer routinely advised for staff or pupils in schools in England and Wales, although they will be required in Scotland until at least the end of September and in Northern Ireland for the first six weeks of term.
Ministers have let it be known they are keen on getting this age group vaccinated – both through public pronouncements and privately behind the scenes.
The argument is that it could reduce school disruption and keep infection levels low.
But there’s still plenty to consider. Giving this age group jabs would mean time out of class and possibly off school recovering from common side effects such as a mild fever.
This is not like the flu jab, which is a simple nasal spray.
Its ability to curb spread may be less than first assumed too. It is thought about half of this age group may have been infected already and therefore have natural immunity.
The emergence of the Delta variant also means the vaccine is less effective at stopping infection than previously – its main benefit is to prevent serious disease and as these healthy children are at incredibly low risk of that the benefits, as the JCVI points out, are marginal.
It is worth remembering that there are six million adults – twice the number in this age group – who still remain completely unvaccinated.