Too much …

Is it possible to give students too much help?  I had an interesting experience this past week – midterm #1, much the same as I have done for the past 4 years.  Same level of difficulty, same topic coverage.  One major change – I made it open book.  Students could bring in the text, their notes, and even last year’s exam with the solutions.  Why open book?  I wanted to remove the necessity of memorizing facts. I had already told students that the exam would be similar to last year’s so there weren’t any surprises.  Well, one major surprise on my part … How did some students fail to achieve competency?  I know that test-writing is one of my weaknesses, I know that time was tight.  Was it a bad test?  After a lot of thought this weekend, I’m confident that the test itself was not the problem.  I’m wondering if students delayed learning the material since it was open book.  Sort of a false sense of security .. too much security.  Just a conjecture and I don’t have any empirical evidence.  What are your thoughts?