Sankey set league and district season and career running marks as a senior. He rushed for 2,518 yards and 33 touchdowns on 281 attempts (8.96 yards per carry), becoming the first athlete in district history to have two "top ten" running seasons. His 33 scores are also a district record. As a junior, Sankey led Bishop Gorman to its first-ever undefeated regular season (10-0) and was named Las Vegas Review-Journal Player of the Year after he ran for 1,929 yards and 28 touchdowns. As a sophomore, he became the first player in school history to earn first-team all-state honors from the Nevada State Football Coaches Association. He finished his high school career with 7,244 yards and 91 touchdowns on 881 carries (10.01 ypc). He committed to Utah Utes to play football under head coach Kyle Whittingham. "I just felt like they were the best fit for me," he said. "I really like what they're doing over there. They're going to a 4-3 defense which is something I can get used to." During his high school career, Sankey had more than 100 yards rushing in 23 of 27 games played. He had three games with 200 or more yards and four other occasions where he reached the century mark.