The best dispatcher training (with outstanding reputation with airlines) is Sheffield School of Aeronautics. They are known by US airlines and foreign air carriers as well. They are located in Ft. Lauderdale, FL, and their training takes some 8 weeks. The cost in approximately $5,000, all inclusive. Several sessions are available each calendar year. See their website.
I studied for my FAA licence at Sheffield & I have to say, it is without doubt, the most comprehensive training program possible for our line of work. The instructor, (Brett) is probably the most knowledgeable man in the business whom I've had the pleasure of being taught by & I've been around tin a long time so I don't say that lightly.
My only gripe with the FAA is the distraction of ADX...

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Any other school
will fall short by their standards....By at least the definition of a ceiling + infinity.....Or a high min captain's destination RVR requirement!!