Smaller is better, particularly when you’re talking about a projector that needs to travel from room to room throughout the school day. Take Acer’s C205, an LED powered projector that weighs just half a pound and fits into a backpack or briefcase. The projector puts out 200 lumens at 854 x 480 resolution. Youc an run it off of an AC outlet or its built-in battery and the projector has an HDMI input. It costs $350.