Always mark everything. I was at a class and right after it was over a lady said she was missing 2 rulers. Only about 3 people had to leave early. Two different ladies told me that this had happened before but only if this one person (that had left early) was in a class. I was so shocked! Guess it show naive I am.They told me something ALWAYS turns up missing when this lady takes a class.They all watch their stuff like a hawk which I don't blame them but it sure took the fun out of the class for me. As a matter of fact I haven't taken a class since now that I think of it.