Students in a lab at Signature School, a charter school in Evansville, Ind. (Photo by Terry W. Hughes/Courtesy of Signature School)

America’s Most Challenging High Schools ranks schools through an index invented by Washington Post education columnist Jay Mathews. The index formula is a simple ratio: the number of Advanced Placement, International Baccalaureate and Advanced International Certificate of Education tests given at a school in 2014, divided by the number of graduates that year.

[Read about the method behind The Washington Post’s America’s Most Challenging High Schools rankings.]

Noted in our national and local tables are the percentage of students eligible for government meal subsidies — a common benchmark for poverty — and each school’s average scores on the SAT, a common college entrance exam with a national average of 1497 out of 2400.

The Challenge Index considers college test participation a better measure of school success than test scores, which largely reflect parental income. Schools with ratios of 1.000 or above make the list.

[Many U.S. schools still resist challenging all their students.]

The list has grown to include more than 2,300 schools across the country and more than 175 schools in the Washington region. It includes some private schools — noted with a (P) — for comparison. Certain public schools with highly selective admissions are omitted from the list, but information about them can be found on a separate list.

[Top performing schools with elite students.]

Below are the national rankings for the top 25 schools in the The Washington Post’s America’s Most Challenging High Schools list.

1. BASIS Oro Valley
Oro Valley, Ariz.
Rating: 20.44
Meals Subsidy %: n/a
Average SAT score: 1968

2. BASIS Chandler
Chandler, Ariz.
Rating: 20.07
Meals Subsidy %: n/a
Average SAT score: 1996

3. Talented and Gifted
Rating: 17.77
Meals Subsidy %: 26
Average SAT score: 1923

4. Science/Engineering Magnet
Rating: 17.29
Meals Subsidy %: 65
Average SAT score: 1784

5. Accelerated Elementary and Secondary
Tucson, Ariz.
Rating: 16.00
Meals Subsidy %: 42
Average SAT score: 1895

6. BASIS Tucson North
Tucson, Ariz.
Rating: 14.93
Meals Subsidy %: n/a
Average SAT score: 1939

7. Darnell-Cookman School of the Medical Arts
Jacksonville, Fla.
Rating: 14.82
Meals Subsidy %: 25
Average SAT score: 1522

8. Stanton College Prep
Jacksonville, Fla.
Rating: 14.58
Meals Subsidy %: 14
Average SAT score: 1788

9. Carnegie Vanguard
Rating: 14.12
Meals Subsidy %: 22
Average SAT score: 1895

10. Signature
Evansville, Ind.
Rating: 13.94
Meals Subsidy %: 10
Average SAT score: 1258

11. Jefferson County IB
Irondale, Ala.
Rating: 12.17
Meals Subsidy %: 16
Average SAT score: 1920

12. Suncoast Community
Riviera Beach, Fla.
Rating: 12.42
Meals Subsidy %: 19
Average SAT score: 1734

13. Talkington School for Young Women Leaders
Lubbock, Tex.
Rating: 12.35
Meals Subsidy %: 99
Average SAT score: 1385

14. Paxson School for Advanced Studies
Jacksonville, Fla.
Rating: 11.48
Meals Subsidy %: 26
Average SAT score: 1603

15. Rangel Young Women’s Leadership School
Rating: 11.47
Meals Subsidy %: 11.47
Average SAT score: 1580

16. Archimedean Upper Conservatory
Rating: 10.77
Meals Subsidy %: 47
Average SAT score: 1774

17. Uplift Education Summit Preparatory
Arlington, Tex.
Rating: 10.75
Meals Subsidy %: 72
Average SAT score: 1657

18. Young Women’s Prep
Rating: 10.10
Meals Subsidy %: 67
Average SAT score: 1550

19. Ann Richards School for Young Woman Leaders
Rating: 9.94
Meals Subsidy %: 60
Average SAT score: 1612

20. Corbett
Corbett, Ore.
Rating: 9.90
Meals Subsidy %: 36
Average SAT score: 1497

21. Preuss School UCSD
La Jolla, Calif.
Rating: 9.77
Meals Subsidy %: 100
Average SAT score: 1507

22. Boca Raton Community
Boca Raton, Fla.
Rating: 9.32
Meals Subsidy %: 33
Average SAT score: 1586

23. Keystone (P)
San Antonio
Rating: 9.29
Meals Subsidy %: n/a
Average SAT score: 2132

24. Uplift Education North Hills Preparatory
Irving, Tex.
Rating: 9.23
Meals Subsidy %: 11
Average SAT score: 1747

25. Science Academy of South Texas
Mercedes, Tex.
Rating: 9.06
Meals Subsidy %: 43
Average SAT score: n/a

[See the full national and regional lists.]