There is no evidence boys develop academic ability later than girls, the Equal Opportunities Commission said.
Dr Priscilla Chung Ka-tak, the commission's director on gender issues, said the Education Department had produced no research to support the assertion.
'This is just their observation,' Dr Chung said.
The department has said one of the reasons boys and girls were assessed separately for secondary school places was because boys developed later and needed to be protected to ensure they had equal opportunities in later life.
An expert panel, appointed by the commission, said studies had showed that boys and girls developed in different areas rather than at different times.
The commission also found no intellectual growth spurt among boys between Primary Five and Form Three, according to their English and mathematics test results.
