Hardware
The VR device must be suitable for the learning objectives. Not all are. Simply having a VR device does not mean you have a solution. 3 DoF vs 6 DoF is the major decision here, among a few other considerations. Too many have mistakenly bought devices first, then looked for content later. This is not a sensible approach.
Content
The driver behind any solution is the content, but without the right way to view/interact with the content, you will not be getting what you hoped for. Thus the reason why content is #2, in this list. Interactive content, and lots of it, increases engagement and drives learning toward higher order thinking skills (HOTS).
Online/offline
The easist path forward for a content provider is to have a completely online solution. This is also the hardest for the user because of the large file sizes inherent with VR content. A more important and compelling solution is offline, available to everyone in the world. Don't get fooled by "offline-ish" (go to the Learn More page to... well... learn more).
Ease of use
Mass adoption of a technology, across a wide spectrum of users, is dependent upon an ease of use by both learner and instructor, IT departments, and administration.
Learning is learning
Almost all learning can be greatly enhanced by immersion into a virtual environment set up to mimic real-life experiences. This applies to learning math and science, languages, safety training, soft skills, nursing, electrical, and so on. When multiple headsets are deployed at one location, 3 DoF is the only practical, feasible, and sensible solution to attend to such study.
6 DoF is "better"
For high skills training such as: fine motor control manipulation, welding, surgical training, dentistry, jewelry making, and art restoration, 6 DoF may be beneficial, and possibly worth the extra cost (device cost, IT dept time and effort cost, space and real estate cost, privacy cost, increased complexity cost, and so on). Often, this only requires 1-2 headsets.