The Collaborative International Dictionary of English v.0.48:

Coeducation \Co*ed`u*ca"tion\ (?; 135), n.
   An educating together, of different sexes or races; -- now
   used almost exclusively in reference to the education males
   and females together.
   [WordNet 1.5 +PJC] -- Co*ed`u*ca"tion*al, a.
   [1913 Webster]

WordNet (r) 3.0 (2006):

coeducation
    n 1: education of men and women in the same institutions