NVDA(Non-Visual Desktop Access) is available from nvaccess.org at no cost. NVDA can be run from a portable drive (USB stick) and gives students with visual impairments a way to interact with with their computer. 

This screen reader was designed to be functional and intuitive and continues to be supported by the developers. 

NVDA also comes with OCR (Optical Character Recognition) built-in. Even if a document is not formatted for accessibility NVDA will interpret the image and convert it to readable text.