Cloris herself is also named after her guest star.
EJ's full name is Elanor Josephine Randell.
While clarence is passing by other seniors, the ones that are kissing bear strong resemblance to Percy and Mavis, therefore it is very likely that there one of their grandparents, although it may be unrelated as for example, Percy's Parents do not look as they are related to the character due to some differences.
As Clarence and Cloris crosses the street, a street sign named "Neary”, is a referenced to the Stephen P. Neary, the series showrunner.
It also hinted that as Clarence mentions that Kimby likes Sumo.
The swimming teacher is based off of Pendleton Ward's (creator from Adventure Time) character designs.
Clarence Old Candy Cartoon Network
Clarence Clarence's New (Old) Friend Cartoon Network