The figures for children achieving KS1 Level 3 for 2005 are 23%, 27%, 15%, 23% and 25% for Speaking, Reading, Writing, Maths and Science respectively. The figures are slightly different for Boys and Girls. These are published on the dfes web site:-
Results for other Government KS levels are are published on the site.
You can also get some further information about the KS2 and KS3 Standardistion process on the qca website
Hope this helps