Oher was one of twelve children born to Michael Jerome Williams and Denise Oher. His mother was addicted to crack cocaine since her pregnancy with him. As a result, he received little constructive attention during his formative years. He repeated both first and second grades, and attended eleven different schools during his first nine years as a student. He also alternated between time spent in various foster homes and periods of homelessness, before he was sixteen years old. Oher's estranged father, Michael Williams, a former cell mate of Denise Oher's brother, was murdered while Oher was a senior in high school.
After playing football during his freshman year at a public high school in Memphis, Oher applied for admission to the private Briarcrest Christian School, at the instigation of acquaintance Tony Henderson, with whom he was temporarily living. Henderson was sending his son to the school in order to fulfill the dying wish of the boy's grandmother, and thought Oher might also enroll. The school's football coach submitted Oher's school application to the headmaster, who agreed to accept him if Oher could complete a home study program first. Despite not finishing the program, he was admitted when the headmaster realized that his requirement had removed Oher from the public education system.
After the 2003 football season at Briarcrest, he was named Division II (2A) Lineman of the Year in 2003 and First Team Tennessee All-State. Scout.com rated Oher a five-star recruit and the #5 offensive lineman prospect in the country. During that season and for his prior twenty months at Briarcrest, Oher had been living with several foster families and a football teammate. In 2004, Leigh Anne and Sean Tuohy, a couple with a daughter and son at Briarcrest, allowed Oher to live with them and eventually adopted him. The family began taking care of his needs after becoming familiar with his difficult childhood. They also connected him with a tutor, who worked with him for twenty hours a week. Oher eventually brought his 0.6 grade point average up to a 2.52 GPA by the end of his senior year so he could attend a NCAA Division 1 school by enrolling in some 10-day-long Internet-based courses from Brigham Young University. Taking and passing the internet courses allowed him to replace Ds and Fs earned in earlier school classes, such as English, with As earned via the Internet. This finally raised his graduating GPA over the required limit.