Clark was bumped up to the United States U20 national team at the start of 2002, earning his first cap at that level on January 10 as part of a 1–0 victory over Canada. He was named in the squad for the 2002 C.O.T.I.F. XIX Torneig Internacional, helping the Americans to their best-ever finish; they were defeated by Brazil in the final. Clark closed out 2002 at the CONCACAF U20 qualifying tournament, helping the United States qualify for the 2003 FIFA World Youth Championship. After appearing 28 times for the U20s in 2002, Clark went on to play 19 more games in 2003, including another appearance in L'Alcúdia. His final caps at U20 level came in the United Arab Emirates at the World Youth Championship, where Clark played all five games for the Americans. His 47th and final appearance for the U20s came in a quarterfinal defeat against Argentina on December 12.