 In 2006, over 25% of charter schools in Texas were located in Greater Houston.In 2006, Todd Ziebarth, a researcher of the National Alliance for Public Charter Schools, said that charter schools may have as many as 15% of the market share of students in Greater Houston.During that year Houston Independent School District (HISD) officials estimated that 12,000 to 13,000 pupils living within the HISD boundaries attend state charter schools.