Many segregated schools were overcrowded, and in order to ease overcrowding, the Board instated double-shifts at some schools. Double-shifts meant that students in affected schools attended less than a full day of class. In another measure to alleviate overcrowding at some schools, the Board sanctioned the construction of mobile classroom units. Moreover, a significant proportion of students dropped out before finishing high school. Faculty was segregated, and many teachers in predominantly black schools lacked full-time teaching experience compared to teachers in white schools. In addition, the history curriculum did not mention African Americans. According to CORE, "school segregation a damaging bacteria, a psychological handicap, which [festered a disease generating widespread unemployment and crime in Chicago".