Start by determining what kind of environment your digital projectors will be used in. Will the images have to be bright enough to be seen in full-room lighting? Are there windows that will allow in sunlight as well? Or will they be used in dimmed surroundings?
A rule of thumb: In most cases, a digital projector that provides 1600-2000 lumens of light will be sufficient for normally lit rooms.
Once you know what kind of lighting conditions the digital projectors will be operating in, the next choice is resolution. The economical SVGA is good enough, but XGA is best when the images need to be blown up to serve large rooms and when the images must be extremely detailed.
Should your digital projector be portable or built-in? If it is portable, the unit can be shared between rooms. However, portable projectors are light and small enough to be easily stolen. If theft is an issue in your schools, consider permanently mounting your digital projector in a specific classroom.
Save money by having digital projectors serve multiple purposes. These can include acting as large-format computer displays, TV monitors, and document camera displays.
Extend bulb life by operating digital projectors at their lower light settings where possible.
Both DLP and LCD digital projectors provide comparable image quality at comparable prices. Decide for yourself which is best by having one of each made available for side-by-side testing.