The education secretary has vowed to tackle persistent pupil absences "head on", describing it as a "key priority".
In a speech to head teachers on Saturday, Nadhim Zahawi said disadvantaged children lose out most from not being in school.
Ahead of the spending review later this month, he pledged to invest "record sums" in children's education.
It comes after the number of pupils in England absent for Covid-related reasons rose two-thirds in a fortnight.
The latest government figures showed 204,000 children - 2.5% of state school pupils in England - were out of school for this reason in the fortnight to 30 September.
There are also concerns children may be missing lessons because of mental health issues.
Speaking at the conference of the NAHT school leaders' union in London, Mr Zahawi said: "Another key priority for me will be getting to the root of what is causing children to be persistently absent and then tackling it head on.
"Because the children who lose out the most from not being in school are likely to be the ones who can cope least - the vulnerable, the disadvantaged. You can't help them if they aren't there.
"For all these reasons, we will continue to invest record sums in our children's education."
He added that he would not give a "running commentary" on the spending review, but said he would "not stop" making the case for investing in children and young people.
He also called for better understanding of and support for mental health issues.
"I want us to put wellbeing at the centre of everything we do in schools alongside a drive for rigorous standards and high performance. But, of course, we can't do this if children are not at school," he added.
In response to the education secretary's comments, Paul Whiteman, NAHT's general secretary, said Mr Zahawi needed to match the "passion and ambition" of school leaders.
"The real test though, is what he is prepared to do immediately, to prise more investment from the Treasury in the comprehensive spending review, and then how he chooses to develop policy in the coming weeks and months," he said.
Addressing the conference on Friday, Mr Whiteman said the government's goals for helping children catch-up after the pandemic needed to be more ambitious.
"Recovery implies a return to what we had before, which is simply not good enough," he added.
In June, the government's schools catch-up tsar Sir Kevan Collins resigned, saying the £1.4bn in funding pledged to help pupils make up for lost learning fell "far short of what is needed".