Superintendent Richard Carranza's tenure in Houston ISD was not only among the shortest in recent history for Texas' largest school district -- it was much shorter than the average tenure of superintendents leading large, urban school districts.

A 2014 study by the Council of Great City Schools found that the average tenure of immediate past superintendents was 4.5 years in 2014. Carranza's tenure of 18 months is about a third as long as that average.