Superintendent Carol Johnson said that the school system, tries to make evaluations “fair and consistent.” Globe/File

The Boston Teachers Union demanded Tuesday that the School Department launch an independent review of its new teacher evaluation system to determine why black and ­Hispanic teachers are more likely to be targeted for possible dismissal.

Union officials made the ­request after analyzing School Department data and finding that black teachers were three times more likely than white teachers to be placed on a ­”directed growth plan” or an “improvement plan,” a move that can lead to termination if an evaluator determines a teacher has failed to overcome shortcomings in the classroom.

Similarly, Hispanic teachers are 1½ times more likely than white teachers to be placed on one of those plans, according to the union analysis.

“It’s deplorable,” said Richard Stutman, the union’s president, who derided the new evaluation system as overly subjective and unfair. “I don’t know how [the School Department] can defend a system that is disproportionately identifying black and Hispanic teachers.”

School officials acknowledged Tuesday that they ­noticed a similar trend when they reviewed their data and said they intend to probe deeper and might tap outside expertise.

“We are concerned about it,” said Superintendent Carol R. Johnson. “We want to make sure when we do evaluations they are fair and consistent. . . . Our goal is to help teachers as much as possible.”

Johnson also cautioned against drawing broad conclusions about the data, adding that the numbers are small and could change significantly as the School Department completes its evaluation of teachers under the new system.

The School Department has finished evaluating about half of its 4,839 teachers, and the rest will be completed by the end of the school year.

So far, 140 teachers have been placed on either a self-directed or improvement plan, and 46 teachers are facing termination, according to the union analysis.

Among all black teachers – regardless if they have been evaluated or not – 68, or 5.9 percent, are on one of the plans; among white teachers, 53, or 1.8 percent, have a plan; and among Hispanic teachers, 14, or 2.8 percent, are on one, the union said.

The School Department ­adopted the new evaluation system in September, the culmination of tense negotiations with the union that almost had to be settled by a state labor ­mediator.

The evaluation system, created to comply with updated state regulations, also applies to administrators and aims to bolster the quality of classroom ­instruction and school leadership. The concept is that even the most talented educators should identify annual goals to work to improve their craft.

But the new system also ­attempts to crack down on poor performance. Educators deemed unsatisfactory can lose their jobs in less than a year.

Under the new system, all teachers are subject to multiple observations over the school year and must receive feedback shortly after each one. Teachers are also encouraged to submit via computer a wide range of artifacts demonstrating their performance, such as lesson plans and examples of student work.

Teachers can receive one of four ratings: exemplary, proficient, needs improvement, or unsatisfactory.

Stutman said the system gives administrators too much discretion in judging performance.

“Why is it falling the way it is falling along racial lines?” asked Stutman. “I think it does call for an outside review.”

Johnson defended the integrity of the new system, arguing that it is far more objective than the old system, which often failed to define expectations for teachers.

Under the old system, teachers were only identified as meeting standards or being unsatisfactory, if schools bothered to do the evaluations at all, and did little to identify teachers who may need some extra help or those who could be models for other teachers.

“I don’t think it is fair for the union to discredit our evaluation system as a whole,” said Johnson. “We want to make sure our workforce is really ­diverse, and we want to make sure students get the best teacher in the classroom. That is work we are doing under the new evaluation system.”

The School Department has been under pressure from the City Council and city youth ­organizations to increase the ­diversity of its teaching ranks. While 76 percent of students are black or Hispanic, 63 percent of the teachers are white.

The School Department has had better luck with its principals, 55 percent of whom are black, Hispanic, or Asian.

Johnson said that she is committed to increasing diversity of the teaching force and that a committee has been meeting for a year now to identify additional supports for teachers of color and devise ways to recruit more of them to the Boston schools.

James Vaznis can be reached at jvaznis@globe.com. Follow him on Twitter @globevaznis.