The D.C. schools continue to be one of the worst places to learn and hardest places to teach in America, but its leaders are making sensible, if slow, changes in the right direction. The latest smart adjustments are in teacher evaluation.

Many teachers I admire have trouble with the rating system known as IMPACT. They don’t like the unpredictability of the evaluations by classroom assessors called Master Educators. They don’t like the statistical weirdness that can distort the student test score gains that affect their ratings. They think some of the activities on which they are graded don’t make sense.

But I don’t hear anyone arguing that we should return to the days when more than 90 percent of D.C. teachers received satisfactory evaluations while the achievement levels of D.C. students were among the nation’s worst. The low test scores were not all the teachers’ fault, but no sane observer of city schools would say that more than 90 percent of instructors were doing fine.

Under the D.C. system’s mix of classroom visits and student-test-score gain assessments in the most recent school year, only 68 percent of teachers were rated effective or higher. That is a change for the better. The District has become one of the few school systems in which teachers who are not doing their jobs can be quickly removed. Now it needs to work on making sure it is helping teachers improve and dismissing only those who should be dismissed.

I have spent three decades studying why some schools produce more learning and better teacher morale than others. The best schools almost all share one advantage — a smart and energetic principal who has the power to hire teachers, assess them and pay or fire them accordingly. The schools work as teams, trading tips every day. They have bad years, like all schools do, but know how to identify and fix their problems.

The D.C. system doesn’t do enough to create those situations because, although principals have more control over their staffs than in the past, the reliance on test-score gains and Master Teacher evaluations limits their ability to create the best team. The latest adjustments in IMPACT thankfully give principals more power.

The most important change is reducing the weight of test-score gains in a teacher’s evaluation score from 50 to 35 percent. Henceforth, according to a D.C. schools summary, “for the other 15 percent, each teacher will work with her or his principal to collaboratively select an assessment and set learning goals against which the teacher will be evaluated.”

The new rules give principals another boost by saying that from now on “teachers in their first year in DCPS will receive an informal administrator observation before they receive any formal observations.” That allows principals to set the tone for assessments with new teachers. It might also help them influence how the Master Educators do their ratings, if principals make the smart move of befriending those outside evaluators. The new rules also reduce the number of times principals have to evaluate the classroom skills of the best teachers. School officials say this will “free up more time for principals to support struggling teachers.”

This puts greater weight, of course, on recruiting, selecting and training principals so they can create the ideal school atmosphere. The District won’t be able to junk the costly and distracting Master Educator and test gains parts of the rating system until the principals are all top-notch.

Jason Kamras, who oversees the ratings, says more principal recruitment is underway. A training program for 25 principals at Georgetown University and an internal principal development program begin in January. They better work, or the District’s steady improvement is not likely to last.