Timed Interaction in Storyline

Don't say anything about needing to click a number of objects.  Structure it so that they can tell if they are doing something useful or correct.

Every slide or so should have a meaningful interaction, one that gives more information, or treats the click as a response where you can give on the fly feed back.

I would have a progress bar that will advance when they make a correct, or meaningful interaction. Create this in the project template so it will carry over for any slide that uses the template.

One other thing you could do would be to control navigation.  When the user performs successful interactions then can advance to the next slide, or a button appears saying next, or continue.

Use the variable to test, so that way you can see how well a student would progress through the course.  During the initial design i'd have the variable bracketed by Percent signs like " %ClickCount% " showing in the template.  That way you can see numerically how far things advance when you test it out.