"Abstract Art" by Anna Moszynska (ISBN-13: 978-0500202371) comes
highly recomended for teaching the apreciation of abstract art.
"Abstract Expressionism" by Barbara Hess (ISBN-13: 978-3836513852)
Also has a good rating
The are multiple books written about abstract arts. There is a
book "Abstract Art(World of Art)" by Anna Moszynska that is a good
source of information on abstract art.