With in class exams there are several options on what access to background material that students should have:
1. Students can bring any material (texts, notes, assignment solutions).
2. Students can just bring a copy of the text without annotations.
3. Students can bring a one or two page sheet of formulas that they write themselves.
4. The lecturer provides a formula sheet.
Which do you favour?
1. Provides the most realistic "real world" type of assessment, but it can be hard to write new and suitable questions. Given the choice very few students will choose this option.
I have used 2. before. I found it surprising (and disappointing) that I could set questions whose answer could be found in the text but there were still a significant fraction of students who could not do them.
I have been using 3. lately for my solid state physics class (4th year undergraduates). The students hand in their formula sheets with their exam answers. I suspect I started doing this partly to reduce my workload and I thought it would be good revision exercise for the students. However, I am discovering that it is quite revealing to look over the student sheets to see what students do and don't include. Some are very well prepared and others are not. Some don't include fundamental constants they will need and then try to use this as an excuse for not completing a question.
The student sheets give an idea of how hard it is for students to identify key pieces of knowledge. Some equations are of tangential relevance and key ones are omitted. For example, in a recent exam only 1 out of 7 included Bloch's theorem in their formula sheet. Surely, this is the most important equation in the whole course! This underscores to me that we have to not just tell students what the key facts and concepts are but also (somehow) train them to be able to recognise what is really important.