The actress, best known for playing Mercedes Jones in the TV show, will greet and chat to pupils at the high school which pulls in the most online votes.
Riley is also hosting an essay competition and asking students to write about how they plan to change history - and five winners will be invited to spend the day hanging out with her in New York City.
She says, "One of the greatest things about being an actress is using my voice to help inspire fans to pursue their passions. As we celebrate Black History Month, Verizon Wireless and I are launching the Day In The Life Of A History-Maker campaign. The school with the most votes wins a visit from me!"
Both contests are being held in conjunction with the annual Black History Month in February (12).