Kim Fields' (Tootie) mother on the show is her real life mother, Chip Fields.
After Tootie graduates from Eastland in 1986, she is the last one of the main cast of girls to graduate from Eastland. However, Eastland hasn't appeared on the show since the end of Season 4 and 6 in 1984-1986. The school will become a setting again for the series in its last two episodes in 1988 after Blair buys it and becomes its headmistress.
Tootie's graduation in 1986 means that she started her first year in 1982, which coincided with Joe and Blair's senior year and Natalie's sophomore year. However, Tootie has been at Eastland since 1979. At the very least, Eastland starts teaching girls as early as the sixth grade.