The Prime Minister's promising to put his money where his mouth is, if he's proved wrong over hunger in schools.

Greens co-leader Metiria Turei cited information from KidsCan in the House this afternoon that up to 90 percent of children don't have lunch at school.

John Key responded saying he's been to many more schools in the country than the Greens co-leader.

"I've seen a lot of them munching their way through lots and lots of lunches. If the member wants to come with me to a school, and I'll name the school, and 90% of them don't have lunch, I personally will buy them lunch for the whole year."

Metiria Turei will take John Key up on his invitation.