2009-10: Blake Clarke had 80 points in 58 games skating for the bantam team at Shattuck-St. Mary's school in Faribeault, Minnesota. He scored 33 goals with 47 assists.
2010-11: Clarke skated for the Chicago Mission U16 team in Illinois. In 35 games he scored 15 goals with 19 assists and had 46 penalty minutes. He was selected by Fargo in the 13th round (189th overall) in the 2011 USHL Entry Draft.
2011-12: Clarke appeared in 13 USHL games with Fargo — spending most of the season with the St. Louis Blues U18 midget team — and represented the USA in the 2012 Youth Olympic Games. He scored 1 goal and was -9 with 2 penalty minutes with the Force. In 17 games for the Blues he scored 2 goals with 4 assists and had 6 penalty minutes. Clarke scored 2 goals with 1 assist and was -1 with 4 penalty minutes in four games for the USA at the U17 YOG tournament. He was selected by Brampton in the first round (15th overall) of the 2012 OHL Priority Draft.
2012-13: Clarke attended USA Hockey's Select 16 Festival in the summer before skating in 68 games for Brampton in his first OHL season. Clarke was the second-leading scorer for the Battalion; scoring 19 goals with a team-leading 32 assists and was -2 with 42 penalty minutes. The Battalion finished second in the East Division and lost to Sudbury in a five-game playoff series. Clarke led Brampton in scoring in the series with 3 goals and 3 assists and was -1 with 8 penalty minutes.
2013-14: Clarke participated in USA Hockey's Select 17 Festival in July before returning to the Battalion, who had re-located to North Bay. He skated for Team Mullen in the 2013 USA Hockey All-American Prospects Game in September.