GCSEs and A-levels should be replaced by a national diploma, the Liberal Democrats have said.
More needs to be done to close an "attainment gap", Mr Davey says
They pledged to scrap the National Curriculum after the age of 14 - which would give schools "freedom to teach".
Party spokesperson for education, Ed Davey, also said the government's education reforms would not help raise standards for disadvantaged children.
The government says its school reforms for England will create more "good" schools.
The Liberal Democrats also pledged to provide financial incentives for schools to admit disadvantaged or underperforming pupils.
"Pupil premiums" would fund individual children, for example those eligible for free school meals and those who have under-achieved at primary level.
Mr Davey called the current system of GCSEs and A-levels "unwieldy and not appropriate for the 21st Century".
A system of academic and vocational national diplomas would give students more choice as well as knowledge and know-how, he said.
The Liberal Democrats say the government's planned education reforms for England will not raise achievement among the country's most disadvantaged children.
'Haves and have-nots'
Mr Davey said the gap between the attainment of disadvantaged children and those from middle-class homes was wider now than under the Tories.
He also criticised the proposal in the government's Education White Paper to encourage schools to adopt "trust" status, where an outside body such as a business or faith group, or a federation of schools, forms a trust which controls the school's assets, land and admissions.
Mr Davey said the plans would lead to more schools choosing parents, rather than parents choosing schools.
"By focusing on structures, not standards, Labour are not doing enough to focus on the real problems we face in secondary education today.
"If we are going to close the education attainment gap between the haves and have-nots in England, we need reforms which are tried and tested."
He said his party's proposals would "free teachers to teach, empower pupils with choice and encourage schools with incentives".
He also attacked the government's record on truancy and the low rate of pupils who stay on at school after the age of 16.
Britain has one of the lowest post-16 staying on rates in the developed world. Government statistics show that, in November 2005, 31% of 17-year-olds were not in education or training.
Tony Blair has recently defended the planned school reforms, saying that diversifying the supply of schools would lead to higher standards.