1
general::
A public presentation or display, as in It was a terrible bore, what with their show and tell of every last detail about their trip around the world. This expression originated in the 1940s to describe a learning exercise for young children, in which each child in a group brings some object to show the others and talks about it.
American Heritage Idioms
2
general::
Phrase(s): show and tell
a session where objects are presented and described. (Essentially a kindergarten or grade school activity, but often used figuratively.) • It was a short lecture with lots of show and tell. • I can’t take another show and tell session.
McGrawhill's American Idioms And Phrasal Verbs