ChemThink

ChemThink is a website that I can across this year and am eager to try with my students this year.  Students can sign up for it individually, but if they register as part of your class you can track their progress. 
It's a very simply designed website, but the basic principle is good.  You can assign students various sections of the site based on what you are currently teaching.  They can go through a tutorial if they need a refresher or some more information about the topic or they can go right to the question set.  They have to get 10 questions right before they can more on.  If they miss too many in a row, they will have to restart the problem set.  The questions also increase in difficult as they move through the set.
There is also a feature that allows you to correlate to your textbook.  This make the question sets match up to the chapters in your textbook.

I am looking forward to using it next year as my school doesn't purchase subscriptions to sites like Castle Learning and this looks like is a nice substitute (you know me....anything that is free is great!).

Do you use any online questioning sites with your classes?  What are your favorites?

This post originally appeared in my technology blog The Tech Savvy Science Teacher.