You will be able to control the contrast using the color filters with
Variable Contrast paper.  The trick is trying to find the filter settings
for that enlarger and for each VC paper you use.  Try the paper
manufacturers websites.

I don't know what you mean by "poor contrast" - high? low?  But the problem
is in the filter settings.

 Blue? Do you mean Cyan? Should be Yellow,Magenta and Cyan. Unless it's an
additive head. Then you'd have Red,Blue and Green. I'm going to bet it's
subtractive and uses Yellow,Magenta and Cyan. With no filters in the path
you should be getting around a grade 2. If you want harder add more Magenta.
If you want softer add more Yellow. Odds are your paper either came with a
little sheet describing filter settings or you can download it from paper
company website. It'll likely give you the choice of two colour filters
which are supposed to be speed matched or single colour settings that won't
be speed matched.

  Nick

...

There are a lot of factors that can affect the contrast of a print, and
it's not clear how many of those are controlled in your comparison. For
instance, are you using the same brand and type of paper? Ditto for your
developer, your developer temperature, and your development time? Are you
comparing prints made from the same negatives? Even the lenses on the
enlargers might have an effect on contrast.

I'd first recommend controlling as many of these factors as you can. (You
can probably even swap in your own lens for the one on the school's
enlarger for test purposes.) Once you've done that, be aware that diffuser
enlargers (like the one you've got) often produce prints with lower
contrast than do condenser enlargers. I've no idea if that's what your
school's got, but it might be, and that difference alone could account for
the effect you're seeing. I don't know offhand how much of an effect the
light source color would have, but it might have some effect, too, at
least on variable contrast (VC) papers.

Assuming you're using VC paper, you should be able to increase contrast by
adding magenta filtration, but this will require increasing exposure.
Without a manual, you'll need to guesstimate the amount of increase,
though; you may just need to do a lot of experimenting on a print-by-print
basis. If you're using graded paper, you'll need to switch to a higher
grade to get more contrast.

Crank the Magenta up to 150 and make a print.  How is the contrast?

Take off the lens and shine a lens through it.  Have a look...do you see
lots of haze (is it fogged)?  This can kill contrast.  

Thanks to all for helpful suggestions.  After help from the good professor
at the college, it appears that the problem was a fogged lens.  Any advice
on cleaning?  Somehow, the mess seems to be on the inside of the lens and
seems to need more than a wipe on both sides.

Thanks again!

GD

(http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=29985&item=388017795

The Dichro head has nothing to do with the enlarger's being 23Cll or XL.
23C is the name of the enlarger, the "11" is the version and XL means that
the column raises higher than the standard model.  The Dichro head is on of
several that can be used on the enlarger and comes with its own instruction
manual.  The 23C manual won't show you how to use the color head.   I
bought a 23C XL new in 1977 and  used the standard condenser head (which
has color filter drawers for printing color if you want to!) until just
recently when I found a  Zone VI cold light head and timer (thanks eBay) to
try on it.  The 23Cs are built like tanks- easy to change heads and align,
and will no doubt last at least 500 years longer than any digital printer
on the market!  Many people use VC paper with the color head with excellent
results and with all the used color heads coming on the market– the once
high cost of a color head is not much of an issue  anymore. One word of
caution though on the very nice Beseler/Minolta 45A  color head- Beseler
has run out of their inventory of replacement flash tubes and the maker
hasn't made them for about 15 years.