On the question of "izu" --
Japanese syllables are open (end in a vowel), except for 'n'. It is natural for them to stick in extra syllables for terminal consonants (like the z sound at the end of is) and for consonant clusters (so that "grapefruit juice" becomes gureepufurutojuussu or something equally amusing.)
One thing you might try is teaching them that the consonant frequently gets pushed on to the following word. "Is it" is pronounced like "ih zit" for example.
I would say that, beyond the pronunciation of individual phonemes and the difficulty with the extra syllables, one of the problems is that the rhythm of English is fundamentally different from that of Japanese. English moves from stressed word to stressed word, with the intervening syllables crammed in there any old way. Japanese insists on a fairly equal time for each onsetsu, (and in fact, adding a beat is a common way to add stress to a word.)
What I mean is, consider these English sentences:
"The beautiful mountain appeared transfixed in the distance."
"He can come every Saturday as long as he doesn't have to do any homework in the evenings."
If you say them out loud, you'll find they take about the same amount of time to say, even though the second one has almost twice as many syllables as the first. (I am indebted to the site http://esl.about.com/library/weekly/aa110997.htm
for these examples.)
The reason they take the same amount of time is that their are five major stresses in each one. We place stresses at equal intervals, almost like beat one in music. Japanese doesn't do this. The syllables between one stress and another are timed so that we arrive at the next stress on time. If there are a lot of them, they are pronounced fast and sometimes smeared.
Believe it or not, working on the rhythm of people's speech can make a big difference in how well they are understood. I like to suggest that people speak along with tapes of native English speakers. Not *repeat afterward* but speak along with.
Stress is also about pitch. I have had Japanese people work on the pitch of particular words and tell me it helped them be understood. For instance, a friend just passed her real estate test and said she isn't understood when she said "seller" -- a pretty important word in real estate! So I had her practice the step down in pitch (sell is a higher pitch than er) and that helped.
Anyway, I'm not an expert in accent reduction by any means, but it is something that keeps coming up and I keep learning from the problems my Japanese friends tell me about.
Oh, and I'm glad to hear the schools are getting away from katakana English!
"Give me a fruitful error any time, full of seeds, bursting with its own corrections. You can keep your sterile truth for yourself." -- Vilfredo Pareto