Former education secretary Estelle Morris was taunted by Conservatives after the Government failed to reach targets of 80 per cent of children reaching level 4 in key stage 2 English tests and 75 per cent in maths, a target on which she had staked her job when in the more junior role of schools minister.
Government statistics show that half of schools got 78 per cent of children to level 4 in English and 76 per cent to level 4 in maths.
But among the bottom 5 per cent of schools, the highest score is just 46 per cent of pupils achieving level 4. The national average was 75 per cent in English and 73 per cent in maths.
John Howson, a visiting professor at Oxford Brookes University and a director of Education Data Surveys, said: "There is a significant tail of schools which are achieving significantly worse than everybody else."
The Department for Education and Skills and the Office for Standards in Education will now focus on the weakest schools in a bid to hit the 2004 targets of 85 per cent of pupils getting level 4 in both English and maths.
The DfES has launched a programme of intensive support for the 13 authorities with the poorest performing schools.
And Ofsted has said that from this term, if a school is judged to have serious weaknesses, it will be revisited within eight months. The gap used to be as much as 18 months.
But there will also be more pressure on the most able children.
Demands for "value-added" tables, which show how much schools help children to improve, will be piloted in the primary league tables at the end of this year.
These will help show which schools are doing well in difficult circumstances, and they will also expose those schools which are "coasting": allowing able children to get merely average results.
For the first time this year, schools must set targets for the number of children they expect to reach level 5 in KS2 tests.
John Coe, spokesman for the National Association for Primary Education, said: "The pressures are so great that it would be a remarkable school which said we can just ease along.
"But there are a few schools where, perhaps out of principle, the head or staff may feel that to push children on to higher levels is distorting the quality of education.
"And once they have met targets they are not going to push even harder."