Teachers in 18 D.C. classrooms cheated last year on high-stakes standardized tests, according to the results of an investigation released Friday by the Office of the State Superintendent of Education.

The findings come one day after journalist John Merrow published a 2009 memo that raised questions about whether D.C. officials have adequately investigated past cheating allegations.

The 18 classrooms found to have “critical” violations of test security were spread across 11 schools, including seven traditional and four charter schools. Critical violations include test-tampering such as providing students with answers or using prohibited electronic devices.

Teachers in four other classrooms were found to have committed “moderate” infractions, such as refusal to sign a non-disclosure form.

“DCPS received final information about the OSSE’s test integrity investigation this morning,” said D.C. Schools Chancellor Kaya Henderson in a statement. “At this point, we are not able to make any comment about the specifics of their findings as we have not had a chance to fully review the results of their investigation. But where cheating is confirmed, we will swiftly take the appropriate disciplinary actions.

“We are pleased that this is yet another investigation that confirms that there is no widespread cheating at DCPS,” Henderson added.

The audit was conducted by Alvarez and Marsal, the same firm that last year found cheating by three teachers on the 2011 tests, known as the D.C. Comprehensive Assessment System.

The DC-CAS was administered to students in 2,688 classrooms, according to OSSE. The agency flagged a total of 41 classrooms in 25 schools for extra scrutiny based on odd patterns such as suspicious wrong-to-right erasure marks, unusually big gains or drops in students’ scores or unusual score patterns in a classroom.

Alvarez and Marsal then visited schools and interviewed students, teachers and administrators.

The seven DCPS schools where scores will be invalidated are: Beers Elementary, Brightwood Education Campus, Hendley Elementary, Kenilworth Elementary, Langdon Elementary, Miner Elementary and Winston Education Campus.

The four charters are Arts and Technology Academy, Community Academy-Amos I, Hope Community-Lamond, and Meridian.

D.C. test scores have come under increasing scrutiny since USA Today published a March 2011 investigation showing an unusually high number of erasures from wrong to right answers in more than 100 D.C. public schools from 2008 to 2010