A 16-year-old student said she and Lampley, 28, engaged in a sex act in the athletic training room on Feb. 12.
Officials said they started an investigation after noticing the student had skipped class.
Lampley resigned shortly after accusations came to light. He was a basketball coach at the school.
He faced a possible sentence of five years.
Lampley, of Fairfield, was a senior point guard for the 2003-04 Hamilton High School team that won the Division I state championship. Lampley scored a team-high 16 points in the 51-48 championship game victory against Toledo St. John’s Jesuit to earn the state tournament’s Most Outstanding Player award.
After graduation, Lampley walked on at Ball State and eventually landed a scholarship by his junior season. He earned a degree in education in 2009 and returned to Hamilton City Schools as a district substitute, teaching primarily at Garfield Middle School, where he also coached the eighth-grade Griffins. In 2011, he took a position as an unpaid varsity assistant at Hamilton High School.