A teachers’ union wants to know if shutting schools early before Christmas did anything to bring down the Covid-19 transmission rate in Wales.
The Association of School and College Leaders Cymru (ASCLC) also called for quick action on plans for schooling if cases continued to rise in Wales with a new strain of the virus circulating.
Children are set to return to school in January on a staggered basis.
The Welsh Government said it was closely monitoring transmission rates.
Before Christmas, scientific advice asked families with children to consider “pre-isolating” at home for 10 days before seeing elderly relatives.
The advice was contained in a report by the Welsh Government’s Technical Advisory Group (TAG).
All secondary schools and colleges shut a week early but some counties kept primary schools open until 18 December.
As of 23 December, the R number had increased again to between 1 and 1.3 in Wales, with an estimate from Public Health Wales of 1.2 based on case rates.
This means for every 10 people with the virus, 12 more people would be infected.
“We closed for a week at the end of last term to try to get the R rate down,” said Eithne Hughes, director of the ASCLC.
“Have things changed significantly as a consequence of schools closing?”
Ms Hughes said there needed to be very clear communication if there was any change of plan on schools returning.
“We need to know extremely quickly in order that parents and schools know exactly where they are in a very short space of time,” she added.
The Welsh Government said coronavirus cases “remain very high in Wales”.
A spokeswoman added: “We are closely monitoring the impact of the decisions we have taken to protect people’s health, including the move to alert level four and the decision to provide online learning for the final week of term secondary school and college students.
“Whilst there are encouraging signs that the package of measures introduced in the weeks before Christmas may have had an impact, this is not the case in every area of Wales.
“We would want to see a sustained trend before starting to draw conclusions.”