The State Government has lost track of the whereabouts of more than 1100 schoolchildren.
The Education Department did not disclose the number of missing school-age children in its annual report for this year, even though it has done so in previous years.
In response to a request from The West Australian, the department said the number of school-age children whose whereabouts were unknown was 1129 as at June 29.
This was lower than the 1461 recorded last year but higher than the 813 reported missing in 2009-10.
Statewide services executive director Juanita Healy said there was "no special reason" why the figure had not been published in this year's report.
"At any given time, the number of children whose whereabouts are unknown is available from the department, but it varies from day to day," Ms Healy said. "Should Parliament request certain additional information, it will be included in future annual reports."
The Opposition said this year's report also failed to disclose Aboriginal students' attendance rates, which had been included every year for the past seven years.
Shadow treasurer and acting shadow education minister Ben Wyatt said it was arrogant to remove figures that had been standard in previous annual reports "simply because they are a poor reflection on the Government's performance".
"These are directly linked to cuts that they have made to the education budget, particularly around participation officers," Mr Wyatt said. "It's not just a lack of transparency, but a deliberate attempt to deceive West Australians."
Acting Education Minister John Day said the number of students lost to the system fluctuated constantly because families moved for many reasons - around the State, interstate and overseas - without letting schools know.
He said the figures for children whose whereabouts were unknown were not about attendance rates, participation or truancy, so it was "highly misleading" to associate them with cuts to the number of participation co-ordinators.