Commissioner P. P. Claxton issued a questionnaire to 2,500 teachers, selected through the administrative officers of large city systems asking for the games and exercises which the teachers used in correcting the classes of errors which are given as chapter headers in this bulletin. Detailed responses were received from some 500 teachers. The content of this bulletin illustrates a useful method of improving teaching practice. The compilers believe that if all important problems of teaching were treated in the same manner, by collecting the methods of solution worked out by teachers in the classroom, a great deal of very significant material would be disclosed. [Best copy available has been provided.]