Before  using  a  training  aid,  the  instructor should  be  sure  it  applies  directly  to  the  subject matter and helps achieve the learning objective. The  instructor  should  preview  films  and  ensure that  mechanical  aids  are  in  good  working  order before  they  are  used. Each aid used should present only one basic idea since presenting two or more ideas simulta- neously  may  be  confusing.  To  be  effective,  the aid  should  be  used  in  the  presentation  at  the appropriate  time. The  training  aid  should  be  large  enough  for the most distant student to see it clearly. If the aid is not large enough to display at the front of the classroom, the instructor could ask students to gather around the display so as to get a closer look. Or, the students may be allowed to pass the aid  around  the  room—from  student  to  student. If  this  is  done,  the  instructor  should  allow each student a few moments to examine the aid before  proceeding  with  the  presentation.  When displaying  an  aid,  the  instructor  should  be  sure that  no  student’s  view  is  obstructed. Teaching a Skill One method that is useful for teaching a skill is   the   demonstration-performance   method,   or teaching by doing. This procedure covers all the necessary steps in learning a skill and presents them  in  the  most  effective  order. The  teaching-by-doing  method  of  instruction involves   “doing”  by both the instructor and the student. This method is most effective when a skill is  to  be  taught  to  one  student  or  a  small  group of  students.  Classroom  time  may  not  permit  a group of more than 10 to learn the skill when this method is employed. For a group of 10, breaking the  students  into  2  groups  of  5  each  would probably  be  more  effective. The  order  of  presentation  is  important.  The instructor  should  begin  with  the  purpose  and objectives.  There  is  a  difference  between  seeing and perceiving, so the instructor must take care to explain and stress major points of the presen- tation.  If  nomenclature  is  important,  then  the instructor must name each part and describe its function. The  following  steps  can  be  applied  to  most teaching-by-doing   situations: 1.  The  instructor  does  and  tells. 2.  The  instructor  does  while  a  student  tells. 3.  The  student  does  and  tells. 4.  Students  practice  (under  supervision). 6-10 In  step  1,  the  instructor  performs  the  skill carefully,  accurately,  and  slowly  enough  for the  students  to  follow.  Care  should  be  taken to  emphasize  any  action  the  group  might  miss if   it   were   not   pointed   out.   Applicable   safety precautions  should  be  stressed  and  followed  by the  instructor  at  all  times.  Instructors  should beware  of  the  trap  implied  in  the  statement “I’ve done that so many times I could do it blind- folded.” Perhaps this is a true statement, but it may cause students to ignore safety precautions. The  first  step  is  very  important.  The  presenta- tion must be so organized that no vital information is omitted. Such hesitations or interruptions as “I forgot to tell you . . . ,” or “Just a minute while I check this step,”  would  clearly  indicate  that  the instructor  is  not  properly  prepared. In step 2, the physical steps are completed while a student explains what the instructor is doing. The instructor should perform the steps precisely as directed by the student unless safety precau- tions  are  violated.  Then,  if  an  error  is  made  by the student, the other students (or the instructor) can  point  out  the  mistake.  In  the  event  of  an error, the performance should stop and the error be corrected. Then the performance should start over  again  with  the  student  explaining  the procedure correctly. If there are too many errors, the  instructor  should  stop  the  performance  and repeat step 1 before calling the same student to begin step 2. Step 2 is particularly valuable when there is a chance of harming personnel or damaging equip- ment  while  the  skill  is  being  taught.  The  students demonstrate  orally  that  they  know  what  to  do, but are relieved of the possibility of endangering themselves or the equipment. Students can con- centrate  on  procedure  without  fear  of  injury  or failure.  This  would  apply  in  fire-fighting  train- ing  or  operating  audiovisual  equipment. Step 2 is the time the instructor should ask a number  of  questions  to  be  sure  the  students understand  what  they  are  saying  rather  than simply  repeating  the  instructor’s  words.  Such questions  would  be  as  follows: “What  do  I  do  next?” “How  do  I  do  that?” “What  should  happen  now  that  will  demon- strate  to  me  that  the  steps  I  have  taken  are correct?” “Is  there  anything  I  should  be  careful  of  at this  point?” “Why  do  we  do  it  this  way?”