For the transformation from Developer to Tester (with a development background), my answer here will be oriented towards what can be done in a short amount of time. This will get your Developers acquainted with Software testing quickly, so they can see if Software testing is actually their cup of tea.
Good Software testers are people that really enjoy learning about the domain under test and have a real curiosity about what makes it work. If your students don't like testing after their first month of training, them let them out of your class!
First, I would simply start your students out reading every page of Elisabeth Hendrickson's fine book on Exploratory testing called Explore It!. This will give your students a firm foundation on manual testing, which is the foundation of all good testing.
Second, I would have them start creating automated tests with a functional testing framework like Selenium. You could just have them create tests for their (or your) favorite website.
These two training activities should overlap some, you could start creating automated tests after they have spent the first two weeks on Exploratory Testing study and exercises.
Another book that I would recommend is Debugging by Thinking by Robert Charles Metzger
Metzger's book is very unique in that it approaches how to do testing the way Sherlock Holmes and other fictional detectives might of done it, looking at logic, psychology, engineering, etc.
My thought here is that your developer students will pick up practical testing skills from Hendrickson and foundational thinking skills from Metzger.
Good luck and try to have fun with your students!