I'll give you a couple of thoughts.
Overtime, ink reside will collect both on the bottom of the print heads as well as around the capping station. This is true of all printers. If you don't periodically clean them you will end up with dried ink dragging across the edges of your prints. The way to do that is unplug the printer (always) and take a lint free cotton cloth of some sort dampened with either distilled water, Simple Green cleanser mixed 50%/50% with distilled water or even Windex. Feed the cloth inside the paper compartment, usually by backing it to a sheet of print paper. Pull the head across it several times and watch the black ink transfer to the cloth. Do this as many times as it takes to remove that stuff. Then with a good light look back in the area where the head rests when not printing (capping station) very carefully clean it with damp qtips until it is free of ink. Also clean the wiper blade, that thing that the head runs across just before it stops in the cap station.
A lot of the time this procedure does the trick. Be EXREMELY careful not to get ANY of the electronics on this printer wet. I have blown main boards when working on heads by allowing a little over spray to dampen one of the sensors. If any of these sensors, and there are a lot of them, get wet it will blow your logic board.
Beyond that, when heads eventually wear out you will see these foggy ink dots in the paper margins of your printer or you will see banding in one or more channels that never clears up no matter what you do. If this kind of thing never goes away after all this cleaning you know you need to replace the head. It sounds like with all the use in a school situation that may very well be the case but try the above first if you haven't already. I would clean the bottom of the heads at least every six months.
If you do replace the print head make sure you have them replace the cap/pump assembly at the same time. They generally should be replaced together and could give you a lot of additional life with the printer if you do.
One thing, if you are in a school situation I would always keep the printers under warranty. They are getting harder and harder to work on and for me it just isn't worth the trouble anymore.
John
