Many lecture halls today have two or more screens to be used by instructors for lectures with computer-supported visual aids. Typically, this additional screen real estate is not used to display additional information; rather a single stream of information is projected on all screens. We describe a controlled laboratory study that empirically assesses the effect on students learning of using the increased classroom screen real estate to project an additional stream of information. We measured how well participants learned from a two-stream presentation compared to a one-stream presentation duplicated on both screens. Data indicate that using extra screen real estate can indeed improve learning. In particular, learning was most improved when pertinent prior information was shown alongside currently explained information. There is also evidence that visual comparisons were improved with parallel viewing using extra screen real estate. Subjective data gathered from participants showed a strong preference for learning with two streams of content over a regular one-stream presentation. (Contains 7 tables and 4 figures.)