About one fifth of all Boston public school students whose first language is not English are not receiving adequate educational services, according to the district.

A letter from the federal government – signed by attorneys from the U.S. Department of Justice and U.S. Department of Education earlier this month – highlighted the district’s shortcomings regarding English-as-second language  (ESL) instruction.

The letter, dated March 2, states that just under a quarter of so-called English language learners (ELL) are receiving insufficient instruction, while 49 percent of middle school and high school English language learners are “either without ESL instruction or are receiving an inadequate amount of ESL instruction. ”

“The number of ELL students without adequate services in the interim is concerning,” reads the letter.

The district, according to Boston Public Schools spokeswoman Denise Snyder, is making progress.  She said the district-wide numbers cited by the federal government does not accurately represent the “higher level of services students are receiving.” She said the 49 percent figure in the letter is not accurate. She said 20 percent of English language learners in the district are not receiving all the services “they need and deserve.”

“We are doing significantly better than when first cited in 2010 in supporting our English Language Learners,” said Snyder in an e-mail. “We are not there yet, but our progress can be measured in outcomes such as identifying ELL students and connecting them to proper programs and services.”

The district plans to hire more qualified teachers to address the problem, she said.