International encyclopedia of education  V.7:P-R 
ed.by Torsten Husen, T. Neville Postlethwaite. 
 - Oxford  Pergamon Press  1985 
 - ix, 631p. 
<br/><br/><label>ISBN: </label>0080281192 
<br/><br/><label>Dewey Class. No.: </label>370.321  / N85.7 "R"