A native of Alhambra, California, Wallen won 11 letters at Alhambra High School, including letters in football, tennis, track and basketball. He was also voted the prep Player of the Year in the Pacific League. Wallen enrolled at UCLA in 1955. He was converted by UCLA coach Red Sanders from a wingback to an end. Wallen was a three-year starter at the end position for UCLA in 1956, 1957, and 1958. As a sophomore, he caught 23 passes for 308 yards and two touchdowns.