Complex sentence: Mills attended Urbana High School in Frederick County, Maryland from 1996-2000, where Mills led the team to consecutive 2A state championships in 1998 and 1999, going undefeated both years.
Split into simpler sentences: Mills attended Urbana High School in Frederick County, Maryland from 1996-2000. While at Urbana, Mills led the team to consecutive 2A state championships in 1998 and 1999, going undefeated both years.