That's when the Atlanta educator saw the $365,000 check for the innovative private school he opened in one of the city's poorest neighborhoods in 2007. It was, quite literally, an answer to a prayer.
"We teach school all day and fundraise at night," said Clark, who finds private donors to pay most of the $14,000 annual tuition for each student. "To have an unsolicited gift come like that is incredible."
Clark surprised his students with the news of the donation Wednesday morning in a gathering at the south Atlanta school. The children, parents and teachers erupted in deafening cheers when he showed off the check.
Several cried at the news.
"Everything they learn is enhanced because of the teachers' dedication and creativity," said a tearful Gloria Nesmith, whose son, Cameron, is a fifth-grader at the academy. "And Oprah noticed. I'm just overwhelmed."
The donation, which likely will go to scholarships for students, would pay for 26 children to attend the school for one year, Clark said. The 80-student middle school depends almost entirely on donations to operate.
In her letter, to Clark, Winfrey calls him a role model and applauds the "profound difference you're making with your passion for teaching."
Clark and his students became overnight stars during the presidential election when a video of the students performing a political rap they wrote grabbed the public's attention on YouTube. The children ended up performing the rap, called "Vote However U Like," on national TV shows including CNN and BET.
Teachers at the school frequently use rapping, dancing and drumming to help students learn.
Clark, who taught in one of New York City's toughest schools and wrote the best-selling teaching book "The Essential 55," opened the school last year with proceeds from his book and private donations.
Nearly all of its 80 students are from middle- and low-income households. Parents pay a small part of the tuition and the rest is paid by donors.