what interaction is best for this?

Thanks again Daniel. Worked perfectly. Still, it is very hard for my 68-year-old eyes even to see that disable/enable icon. Sigh. Better than trying to read Adobe screens though. ;-)

Re: the Next button, I want to prevent students from being able to move forward before they are finished with whatever is on the screen. Or maybe with only the version sold to School Boards. I'm thinking university students might want more control over pace, and as most will be student purchases, there is no one to check they've done all the work. 

In some ways I miss working in the corporate milieu ... and in some ways I don't. ;-) 

Thanks for your help. I'm sure I'll be back for more.