It sounds like the first thing you need to do is figure out just what the Perl idioms you're referring to are! For me, the following compose a partial list:

• EVERYTHING HAS USE STRICT AND USE WARNINGS/-w ... Don't go any further unless this is in your curriculum. I know that's being an ass, but I feel that strongly about it.
• $_ and @_ and how they're the defaults. (This is a big one!)
• statement modifiers foo($_) while (1 .. 10);
• grep and map - Spend a lot of time here!
• range operator as a boolean short-circuit
• regexes as pretty much anything (booleans, shortcircuits in ranges, etc)
• Using regexes to parse
• Using substr to parse
• References. Use the pointer concept to start, but break away from it ASAP, as references are NOT pointers.

Basically, make sure they understand TMTOWDI and that their C-Perl is no better or worse than someone else's Java-Perl or my Perl-Perl. :-)

As for getting them to think in Perl, force them into text-manipulation. That's where Perl started and that's where it shines. Ask them to find all the occurrences of a regex-match in a file. Have them do it in their favorite language, then in Perl. Show them 3-4 different ways in Perl, starting with the most C-like, then moving slowly to Perlisms. Try and remember how you discovered things like:

LINE:
while (<INFILE>) {
    next LINE while /Foo/ .. /Bar/;
    chomp;

    # Do stuff here.
}
[download]

How you discovered the idioms is how you want them to discover them ... through iterative runs of the same solution, but written more and more Perlish.

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