A usability lab, while not a necessity, can be a valuable resource for learning how people are using the educational software or websites you have created. A popular combination of tools to use for usability testing is Tobii eye tracking hardware and Morae software for recording mouse movements, etc. Here is an article illustrating how Tobii and Morae can be used in education research.
How much does such a setup cost? A group of students at the University of Washington shared a proposal for a small usability lab that gives an idea. Their proposal totaled about $43,000, which includes Tobii eye tracking hardware ($24,000) and software ($4000). The Morae software runs about $1500.
Perhaps the costs will come down in the future, but there are some open source / open hardware alternatives. The openEyes project out of Iowa State has shared their designs for a mobile eye tracking solution as well as software to analyze the data collected. Here are video demonstrations of openEyes in action. Other computer scientists such as Xiaojun Qi are exploring low cost eye gaze tracking technologies for other purposes than usability research, such as vision-based navigation. For example, what if you navigated a 3D virtual world via eye gaze instead of a mouse, as this group at Queen’s University did.