A Ministry of Education spokesman said the writing test had been revised to make sure it was aligned with the curriculum.
He said feedback from its users had indicated that the marks had been "mostly in keeping with the national norm".
"The ministry is considering what, if any further, action needs to be taken to respond to the results of the review."
The Listener reported that some principals were concerned that less scrupulous schools might not question the higher results or even understand that the results had changed. This could boost their National Standards results and their standing in publicly available league tables.
The writing test was run by the ministry, and the reading test was developed and run by the New Zealand Council for Educational Research.
Its general manager products and services Graeme Cosslett said his organisation stood by its revamped test.
He said it had been trialled on 16,000 students in pilot programmes and national trials over two years.
But he acknowledged that NZCER could have improved its communication with schools over the new reading test.
Asked whether the review was influenced by the ministry, Mr Cosslett said it had been demanded by teachers, not politicians.
"There has been absolutely no political pressure to inflate results from these tests and if there was, we would ignore it and stand by the empirical data gained from the rigorous test development processes we use."
Education Minister Hekia Parata was unavailable for comment yesterday.
The allegations of flawed tests could place greater pressure on the minister and her department, which is dealing with ongoing struggles over the Novopay teacher payroll system.
Testing times
Reading
• Created and run by New Zealand Council for Educational Research in 1999, reviewed in 2009.
• A standardised reading test used to identify students' strengths and weaknesses in primary and intermediate schools.
• Used by teachers to help rank each student against National Standards.
Writing
• An online assessment tool for reading, writing and maths created and run by the Ministry of Education for primary and intermediate schools in 2000.
• Used by teachers to monitor students' progress over time and inform parents of how well their children are doing.
• Used by teachers to help rank each student against National Standards.