Simple English Wikipedia uses "Basic English vocabulary and shorter sentences. This allows people to understand normally complex terms or phrases."
Here's the beginning of its article on Abraham Lincoln (without the links):
Abraham Lincoln (February 12 1809 – April 15 1865) was the 16th President of the United States. He served as president from 1861 to 1865, during the American Civil War. Just six days after most of the Confederate forces had surrendered and the war was ending, John Wilkes Booth assassinated Lincoln. Lincoln has been remembered as the "Great Emancipator" because he worked to end slavery in the United States.. Lincoln was the first president of the United States to be assassinated.Compare that with the first paragraph of the regular Wikipedia's article (again without the links):
Abraham Lincoln Listeni/ˈeɪbrəhæm ˈlɪŋkən/ (February 12, 1809 – April 15, 1865) was the 16th President of the United States, serving from March 1861 until his assassination in April 1865. Lincoln led the United States through its greatest constitutional, military, and moral crisis—the American Civil War—preserving the Union, abolishing slavery, strengthening the national government and modernizing the economy. Reared in a poor family on the western frontier, Lincoln was self-educated, and became a country lawyer, a Whig Party leader, Illinois state legislator during the 1830s, and a one-term member of the United States House of Representatives during the 1840s. He promoted rapid modernization of the economy through banks, railroads and tariffs to encourage the building of factories; he opposed the war with Mexico in 1846.Simple English Wikipedia is simpler, isn't it?
The Simple English Wikipedia doesn't have nearly as many articles as Wikipedia, but if it has one on your student's topic, it could be a big help.