Mike Feinberg and Dave Levin, founders of the KIPP charter school network, produced some of the best middle schools in the country by trying to keep every child safe from harm, including insults. A student who teased another student found herself surrounded by the two tall teachers, who asked if that was really the way she wanted to treat a teammate.

With KIPP having grown to 125 schools in 20 states and the District, including a few high schools, KIPP principals and teachers are finding it harder to create such a peaceful environment for adolescents. This is particularly true in the District. KIPP’s D.C. schools are considered a model for urban public education. But its small high school, KIPP College Prep, expelled 17 students in the 2011-12 school year for violence, weapons and drugs.

The KIPP statistics came from my colleague Emma Brown’s groundbreaking report on the surprising number of students being expelled from D.C. public charter schools. I wrote a book about KIPP and have been visiting its D.C. schools since 2001, so I asked KIPP D.C. Executive Director Susan Schaeffler and KIPP College Prep Principal Jessica Cunningham what was going on.

As independent schools, charters are allowed to expel students, but regular D.C. public schools except in extreme cases (three expulsions last year) can only do involuntary transfers. When I last checked in 2008, the expulsion rate for all KIPP D.C. schools was 1 percent, nine out of 900 students. Last year, that rate was up slightly to 1.4 percent, 39 out of 2,632 students. But expulsions at the high school last year jumped from seven to 17, about 6 percent of the student body, as the school had four serious fights and a drug incident.

Schaeffler said, “We have made changes in our procedures at the high school, things as big as revisions in our demerit system and as seemingly small as changing the procedures for passing periods.”

This school year, Schaeffler put 34-year-old former D.C. teacher Cunningham, one of KIPP’s most successful school leaders, in charge of the high school. Transition time between classes was cut from five minutes to three. Hallway pass rules were changed. Cunningham increased one-on-one meetings between students and their homeroom teachers and instituted a weekly community meeting for each grade, allowing students to share their thoughts with school leaders.

Violence has declined. Only two KIPP College Prep students have been recommended for expulsion this school year. Only 12 students have been expelled so far from all KIPP D.C. schools, just 0.3 percent of enrollment.

Charter school critics have said the expulsion figures in Brown’s report prove charters are keeping their test scores high by kicking out students who don’t do well academically. That is not the case with KIPP, where only students who have endangered other students are forced to leave. But Brown’s article indicates expulsions at other charters are sometimes for tardiness, truancy and dress code violations, which is bad policy.

Brown’s report raised a good question: Why are charters expelling so many students? It also introduced another issue: Why are traditional public schools forced to keep dangerous and disruptive students who make it difficult for other students to learn?

If we knew how to rid such young people of their damaging urges, expulsions would be unnecessary. But we don’t know how to do that consistently. Until we do, serving such students at a school just for them, as some districts do, is the only sensible option. The focus should be on giving the largest number of children a chance to learn, not sparing district leaders from making difficult decisions about students who cannot control themselves.