A BASIS charter school in Scottsdale, Ariz., in 2009. (Laura Segall/The Washington Post)

The top 10 in the new America’s Most Challenging High Schools list, using 2016 data, reveal a startling change in U.S. education since the first list, which used 1996 data.

The 10 most challenging public schools 20 years ago included one Florida magnet (Stanton College Prep), one Maryland semi-magnet (Richard Montgomery), one Virginia admission-by-lottery alternative school (H-B Woodlawn) and seven regular public schools (Brighton, Jericho, Manhasset, Scarsdale, Wheatley, Millburn and Indian Hills) in affluent New York, New Jersey and Ohio neighborhoods.

The new top 10 has no regular neighborhood schools. There is one Texas magnet (Mickey Leland), plus nine charters: one in Indiana (Signature), three BASIS schools in Arizona and five IDEA schools in Texas. All are small, with no graduation class larger than 99.

When I started gathering high school statistics in 1996, public charters were a tiny, uncertain innovation. Now there are nearly 7,000 of them with 3 million students. They are funded with tax dollars, judged by state tests but exempt from some rules that govern regular schools. Most are nonunion. Usually they must accept any child who applies and use a lottery if they don’t have room for all. Most are no better than regular schools, but some have reached unusual levels of achievement, particularly BASIS and IDEA.

BASIS schools have been criticized for scaring off students by requiring at least eight Advanced Placement courses and a passing score on at least one AP test. The schools ask for parent donations and usually have very few students with disabilities or low-income parents.

IDEA schools make similar academic demands. Their students must take 11 AP courses and tests. But unlike BASIS they serve mostly low-income families. I think both networks fill a need for more schools with very high standards, and show what interesting surprises charters can produce. I will focus on BASIS in this column and do the same for IDEA next week.

BASIS critics such as author and former award-winning high school principal Carol Burris note the network’s student attrition, such as a 44 percent drop in enrollment from 9th to 12th grade at the BASIS Phoenix school. They say the BASIS management costs are too high. The fact that BASIS has started for-profit private schools raises the possibility that “the taxpayers of Arizona, along with all U.S. taxpayers [might] be indirectly subsidizing these schools and their expansion,” Burris said in a recent piece on my Washington Post colleague Valerie Strauss’s blog.

Peter Bezanson, chief executive of the company that manages the 24 BASIS nonprofit charters, including one in the District, sent me a detailed response. He said Burris miscalculated the management costs and mischaracterized the relationship among the independent nonprofit board setting policy for the charters, two other for-profit companies managing the seven BASIS private schools and Bezanson’s for-profit company. “There is absolutely no co-mingling of public charter and private school funds,” he said.

Complex, isn’t it? Anyone who wants to see Bezanson’s response should email me at the address below. The Arizona State Board for Charter Schools, which oversees BASIS in that state, has evaluated its financial performance statements as acceptable.

BASIS asks families to donate $1,500 per student per year to support teacher performance bonuses at their school. It is not a requirement, and fewer than half of the families contribute, BASIS officials said.

The most recent BASIS charter re-enrollment figure for each grade from kindergarten to 12th grade was above 87 percent except for ninth grade, which was 63 percent. “At that point,” Bezanson said, “we ask parents to make sure to involve their child in the conversation because the BASIS Diploma requires significant work at the high school level, and student buy-in is essential.”

BASIS has started private schools in McLean, Brooklyn, Manhattan, San Jose and Fremont, Calif., as well as in the Chinese cities of Guangzhou and Shenzhen. The American schools’ annual high school tuition is about $27,000, compared with the $40,000 a year that many prestigious Washington-area privates charge.

Few other charter networks have leapt into such ventures. But the charter movement was founded to inspire innovation, and there is nothing else quite like BASIS in the country today.