The assembly government has been forced to defend the education minister after furious headteachers claimed he had questioned their professional integrity over snow closures.
In a statement last week, Leighton Andrews said the current system for recording absent pupils gave a "perverse incentive" to shut schools in snowy weather to "protect or buoy up" attendance statistics.
New regulations will come into force this autumn that will see schools record pupils unable to attend during bad weather as "not required to attend" rather than absent.
The minister said he was confident that this would mean more schools can stay open in bad weather.
But heads and teaching unions said the comments were "insulting" and an attack on their judgment and integrity.
Caryl Lewis, head of Lewis Girls' Comprehensive School in Ystrad Mynach, said she felt "incensed" by the minister's comments.
"We had snow closure for two weeks prior to an Estyn inspection - an incredibly stressful time and not the best preparation, she said.
"Despite the weather, we opened for every external examination. I really feel these comments are potentially insulting to heads' professional judgments."
Mark Biltcliffe, head of Drury School in Flintshire, closed his school for three days. "I have to take exception to the view that as headteachers we open or close schools with our attendance statistic in our minds; we are more professional than that," he said.
"It was very low on my list of concerns when I made the very difficult decisions this winter, at 7am. Our professionalism and integrity is very important to us."
Chris Keates, general secretary of teaching union NASUWT, said: "The simple fact is that schools did not close in order to avoid a negative slant on their attendance figures but to ensure the safety of pupils and staff by not requiring them to make journeys in treacherous conditions."
Welsh schools closed for an average of four days during the extreme weather conditions in December 2009 and January 2010, according to recent statistics.
Although there were wide variations in the number of school closures across the country, in seven out of the 22 local authorities every school was shut at some point.
An Assembly government spokeswoman said: "Far from being pejorative about the conduct of headteachers, the minister's comments were critical of our systems, which have been counterproductive and unhelpful in terms of the rules they impose on heads."