Accroding to ISLMA, the Abraham Lincoln Readers' Choice Award winner is awarded to the book from that year's master list that earns the highest number of student votes.
For a book to reach the master list, adult and young adult fiction and non-fiction titles must be nominated by teachers or librarians and vetted by the nominations committee. While the popularity of a particular title is important, the overall quality of the work is of primary importance. Each year, a panel of high school librarians, teachers, public librarians and students determines the final master list of twenty titles. Registered schools promote these books and students who have read four or more titles are eligible to vote. See the calendar for the award timeline.
This program is designed to encourage high school students to read for pleasure and to become lifelong readers. The award is named after former President Abraham Lincoln, an avid reader and noted author, is sponsored by ISLMA (Illinois School Library Media Association) and administered by the ALHSBA steering committee.
Source: "Abraham Lincoln Award - Illinois School Library Media ..." 2008. 15 Apr. 2015 <https://www.islma.org/lincoln.htm>