Brennan worked at Great Barr School in Great Barr, Birmingham as a senior staff member. Brennan let it be known that Hillcrest School had "no structures, systems or routines" when she took over in September 2002. In 2002 the school came out of special measures. By the beginning of 2003, Ofsted inspectors described it as "one of the most outstanding schools in the country". One of her recipes for changing that was the introduction of a "house system and a prefectorial system". She introduced formal routines such as pupils standing up when someone walks into the classroom; she also got rid of the bells that sounded the end of each lesson. Other measures included a sin bin or exclusion room where misbehaving pupils could go for a period of isolation from their peers.
On 12 December 2007 it was reported that Brennan and her recent senior management team was under investigation for fraudulent reporting of attendance figures during the time she was headteacher at Hillcrest School and Community College. Dudley Council's investigations ended and the case was passed to the West Midlands PoliceEconomic Crime Team. Brennan was identified in the Dudley report for leading a team of senior managers who EWS investigators claim manipulated registers to make the school appear more successful than it actually was. In their interim report, EWS officers alleged that the records created a false impression of improved attendance which promoted the school's image and resulted in higher pupil numbers. West Midlands Police decided there was no case to pursue. On 13 November 2012 Brennan faced a Teaching Agency professional conduct panel in Coventry with teachers Shelley Derham and Linda Westwood, members of her former senior management team. All faced charges of unacceptable professional conduct. Teaching Agency presenting officer, Bradley Albuery, claimed evidence linked the pair to the “deliberate” misrecording to “pretend attendance was better than it was” and to boost perceptions of Hillcrest School. He said GCSE figures were also distorted from 2004 and 2007 by between two and four per cent showing an “inflation” of results. “It is fanciful to suppose that this headteacher did not know what was going on in her school,” Mr Albuery said. “The evidence suggests these were not occasional errors by teachers. In fact it is true that these three teachers were seen as the reason that the school went from failing to successful, and it was for this Maureen Brennan was made a Dame.” Brennan faced an allegation of failing to ensure pupils received a statutory level of education. The hearing was told how fraud police launched an investigation in 2007, but no charges were brought. This charge was dismissed early in the hearing. All three denied unacceptable professional conduct. The charge of failing to provide an education was dropped and the three were found not to have altered the PLASC return which could have misrecorded achievement in the school. On 28 November 2012, Brennan, along with deputy headteachers Shelley Derham and Linda Westwood, was found guilty of unacceptable professional conduct by the Teaching Agency. The disciplinary hearing heard “inappropriate” alterations were made to attendance registers for some pupils between 2004 and 2007. A Teaching Agency professional conduct panel ruled all three had acted “dishonestly” by changing records. All three had denied making the changes, but later admitted their guilt. The panel also ruled: “The misconduct is of a serious nature falling significantly short of the standards of behaviour required of a teacher".
Departure
In 2017, Brennan bid farewell to the school she was head of for 10 years to take up an executive job at the Matrix Academy Trust which runs 4 schools.
