I created Wordle in the summer of 2008, when kid #1 was 5 years old, and kid #2 wasn't even an idea yet. It was a time of extraordinary energy and focus for me, probably as a result of getting regular sleep and having the odd 3-4 hour block of time for thinking. Now, kid #2 is just about 2 years old, and I have been more or less a distracted heap of parts since he came along. Between being a devoted family guy, and caring very much about my job, I have so little time and energy left that substantive changes to Wordle are out of the question. Also fallen by the wayside is my ability to help folks troubleshoot when things go wrong.
Most of the problems people encounter with Wordle are due to its dependence on the Java Runtime Environment, or just "Java" for short. Java is both a programming language and an enormous piece of software that lets you run programs written in that language. At the time I made Wordle, Java was already kind of disreputable as a good platform for software that works in the browser, as Wordle does. But I stuck with Java because it was the only game in town at the time, with respect to the graphical effects I had in mind. One excellent thing about Java is that it provides guarantees to the person running a Java program (an "applet", as they're called) in a web browser, guarantees about stuff an applet cannot do to you. It can't read or write files on your disk; it can't talk to servers on the internet other than the one from which it was loaded (which you presumably trust enough to have visited); it can't even use your printer without your explicit permission to do so.
Unfortunately, despite these security guarantees, both Microsoft (on the Windows side) and Apple (on the OS X side) have done their best to spread uncertainty and doubt about the safety of Java applets. Internet Explorer is especially pernicious, in that Microsoft implies, through their obtrusive pop-ups and slide-down warnings, and flashing X's and shield icons, that an "unsigned" Java applet (such as Wordle) is somehow a threat. (Signing an applet, for what it's worth, means applying a cryptographic signature that some trusted third party has sold me, so that you know, when you run it, that it came from me. But that should only be necessary when my applet requests permission to perform extraordinary actions outside of an applet's usual safety "sandbox"--something that Wordle does not do.) I have heard from many users, some of whom are technically fluent, that they simply could not find the magical combination of settings and permissions that would make Wordle work for them in Internet Explorer. Apple has pulled Java from OS X "Lion" entirely, making would-be Wordle users search for the installer on Apple's support site.
In an effort to do the most good in the fewest words, I have this general piece of advice: if you're using Internet Explorer, download Mozilla Firefox or Google Chrome and use one of those instead. I prefer Chrome for its speed and for various technical reasons, but either is an enormous improvement over IE. Many of the aggravating and seemingly intractable problems people have with Wordle are solved by such a switch. Good news: Chrome also works on OS X, although, as far as I know, Safari works fine. But in any case, OS X Lion users will need to install the Java Runtime Environment, which I understand can be done by navigating to "Applications > Utilities > Java Preferences".
For general help and advice on using Wordle, there's the Wordle Users Google group, which can be used either over email or via a web interface. Over the years, a couple of different people (whom I don't know) have been very generous with their time and expertise in helping new users to untangle Wordle's sometimes confusing behaviors.
Finally, and with all the respect due to teachers, whom I revere and consider to be the underpaid champions of our future: I wish you wouldn't assign Wordle as homework. It results in angry emails to me from kids and (especially) their parents, who are understandably frustrated when they can't get it to work, and feel under the gun to do so.
Many words to say few things! If only there were some way to distill such a long text.