Your son should not lose confidence in his math ability or become turned off. While dealing with the school situation, I suggest supplementing his math education with an online program such as EPGY or Alcumus http://www.artofproblemsolving.com/Alcumus/Introduction.php or Thinkwell . Computerized math programs advance students to new topics when they get the right answers, so "showing the work" will not be an issue.

"To see what is in front of one's nose needs a constant struggle." - George Orwell