Queen Elizabeth II is now officially Britain’s longest reigning monarch. On 9 September, 2015, she overtook Queen Victoria, who reigned for 63 years, seven months and two days, from 1837 to 1901.
The BBC site has a summary article about the Queen’s reign. It's B2 level, but elements such as the comparison between Elizabeth and Victoria at the end are simpler.
A photo feature, with an image for each year of her reign can be used with any level.
There is also a pupil-friendly article from Newsround, with a short film about events during her lifetime. You could use these from A2, or just the images from A1.
The British Monarchy site has a lot of information.
Don't miss our resources on Buckingham Palace below.