Hoag was medical director of the public schools in Berkeley, California. As Hoag wrote in his introduction, the object of this work was "to show teachers and parents how to detect easily those ordinary physical defects of the child which bar his progress in school and life, and to suggest means by which such defects may be removed and good health afterwards maintained. Incidentally it may prove of some value to physicians who are for the first time applying themselves to this special sort of Public Health work." Digital facsimile from Google Books at this link.