Carnegie Vanguard High School has been named to a select group of the top 10 best schools in the nation in two recent surveys.

U.S. News & World Report has ranked the HISD school No. 6 in its 2015 Best High Schools rankings, released this week. The school was up from No. 23 on last year's list. Two other Houston schools were in the Top 100 — DeBakey High School for Health Professions, at 23rd, and Eastwood Academy, at 53rd.

The U.S. News rankings examined 21,000 public high schools in 50 states and the District of Columbia. Schools were awarded gold, silver or bronze medals based on their performance on state assessments and how well they prepare students for college.

For the fourth consecutive year, the School for the Talented and Gifted in Dallas was ranked as the No. 1 public high school in the country in the U.S. News survey.

A recent report by the Washington Post ranked Carnegie Vanguard as the ninth most challenging school in the nation.

The yearly Challenge Index report, which surveyed more than 2,300 schools nationwide, included over 40 schools in Houston. Others on the list include Eastwood Academy (No. 69), Challenge Early College High School (No. 85), Energized for STEM Academy (No. 90) and High School for Law Enforcement and Criminal Justice (No. 93).

The formula takes the number of college-level exams and divides it by the number of graduated seniors each year. The exams are the Advanced Placement exams, the International Baccalaureate and the Advanced International Certificate of Education, which all qualify students for college credit.