Criminal charges are expected to be filed today in connection with alleged cheating on standardized tests in the Philadelphia School District, a source told the Daily News yesterday.

The specific charges and the number of people who will face charges were unclear last night.

The district launched an investigation in early 2012 into allegations of cheating on 2009, 2010 and 2011 Pennsylvania System of School Assessment (PSSA) exams. A state-commissioned analysis of the tests in 2009 showed statistically improbable test scores and a pattern of suspicious erasures at 53 district schools and several others across the state. The state launched a probe of 14 so-called Tier One schools, including three charters, while the district probed 19 so-called Tier Two schools.

Of the 19 schools investigated by the district, 13 were found to have evidence of cheating, three were cleared of wrongdoing and evidence was inconclusive at three others.

In January, the district fired three principals and disciplined 66 current and former employees for their alleged involvement.