In a crowded school computer lab, on a fixed schedule, with blocking software active on their browsers?
At work, perhaps from behind a firewall that treats JavaScript as a security threat?
At home, at the end of a demanding day?
How much time are they likely to have? How convenient is it for them to use certain local resources like books or equipment?
A little effort to find out exactly what your users are dealing with locally can result in a better designed resource that is more heavily used. Research typical usage, meet with advisors who have worked with your target audience, or recruit a few prototypical users to consult with during development.
But even your educated guesses can go a long way toward settling some of your open questions about instructional design.
