Parents are being urged to look beyond the "very immature" information published as part of Fairfax Media's "School Report".
Principals Federation president Paul Drummond warned that some schools could suffer. "Some parents will not see the full context, they will just see the numbers."
Drummond said focusing on the data would be a mistake: "If we become so obsessed with that information, there is a real risk of losing some of the richness of our curriculum."
Controversy erupted after the national standards results of more than 1000 schools from across the country were revealed by Fairfax Media, publishers of the Sunday Star-Times, as part of yesterday's launch of the "School Report" site.
It was the first time the figures had been released, and they confirmed that boys are lagging behind girls in primary school, and there is a chasm in literacy levels between boys and girls as young as five.
The figures show 39 per cent of boys are writing below or well below the standard, lagging well behind girls - a situation mirrored in the reading standards.
The results have prompted calls for a national strategy to help boys.
Leading boys' education expert Joseph Driessen said he was not surprised by the results.
The reason for the gap, and possible solutions, should be investigated, he said.
"Individual schools are doing what they can. Those that try to target it can make a terrific difference."
There were a number of reasons why boys typically underperformed in writing, ranging from a lack of engagement to poor motor skills. "Boys are much more impatient about doing things for the sake of doing things, they like to see results," he said.
And boys often didn't connect reading with being a real man. They associated masculinity with sport, but reading and writing were "for sissies".
But he did not see the current national standards system as a solution. "Unfortunately we keep importing the worst aspects of the English education system into New Zealand. We insist on putting all our children in a single-scale assessment system. We have a very unsophisticated and cheap system, and it will fail children who are disadvantaged or come from poor families."
Although the School Report website included some context to put national standards into perspective, "this is a very immature set of information", that risked being interpreted in the wrong way, he said.
"It is very new and the fact this data is being used for comparative purposes means it will be seen in a simple way. Many people will see it as a measure of a school's success, and that's very one-dimensional."
But he said schools could support national standards if the data was kept between them and the Government.
"If the information was protected within the schools, with a strong responsibility to report to their communities and the Education Review Office, then the high stakes would be taken out of the data."
- Sunday Star Times