Abstract: This study analyzes data from the 2004-05 school year related to the characteristics of Colorado's charter schools, including student achievement. Charter students generally made larger gains in reading, writing, math and science in the past three years than students in traditional schools. Elementary public charter school students did better academically than students in traditional public schools. Charter and non-charter students generally scored similarly within the middle school years in reading and math. Charter high school students performed below non-charter school students in writing, reading and math in the high school years. Researchers found that high school charters in the state seek to enroll students considered to be at-risk. Charter schools are an increasingly popular choice for families in Colorado. Since 2001-02, charter school student enrollment has increased by 49.5 percent.