In some parts of the country as many as 15% of 11-year-olds are four years behind in their reading skills.
These maps of local authorities in England show the percentage of boys who got below Level 3 in their Key Stage 2 tests this year according to figures from the Department For Education.
Level 4 is the government's expectation for 11-year-olds. Level 2 is what's expected of seven-year-olds.
In some areas so many schools boycotted the tests that the authority data is not available.