First suggestion is checking to make sure that the tray/chains are secure - that it's not going to fail at at a point of connection either at the ceiling or point where the chains fasten to the tray. The tray must be strong enough for the weight of the projector (most InFocus classroom projectors are not that bulky and heavy).
Hanging anything with weight from the suspension ceiling braces is not recommended. If possible, having the wire/chain continue thru the ceiling panel (a small inconspicuous hole can be made through the panel) up to actual ceiling joists or whatever material the ceiling system itself is fastened to is best & the most secure. I've used steel aircraft cable (available at any Home Depot or hardware store) in place of chain, partly because it only requires a small pencil-sized hole thru the ceiling panel, hardly noticeable.
Most hanging fixtures (theatrical lights, projectors, etc.) have a secondary/backup safety cable or strap system should the main fasteners fail. In this case, if the tray and ceiling connection is secure, a safety strap holding the projector onto the tray so it's not sitting up there loose or able to be knocked out at all should be used. This also will help keep the projector's aim aligned to your screen should something bump the tray, you won't have to readjust it. (See this link
attached for an example of a strap securing a projector).
(In all cases, if you have a building or school district maintenance administrator or someone who's job description requires them to be aware of state or district safety regulations/OHSA rules, they should be consulted to make sure you're following any safety issues that may apply specific to your classroom/student needs.)