What's the best way to assess a source written by a historian in an exam?

It's really important that in an exam situation you read the sources very carefully; it's far too tempting to race through and miss what the historian is trying to say. When the exam starts, put your pen down and read the three sources through without making any notes, just to ensure that you've read them properly. Once this is done, take each source individually and go through highlighting its defining arguments and points. Then take the three arguments from the source which you believe you would have the most to say about in terms of your own supporting knowledge, and assess them according to whether you think they are convincing or unconvincing. For each source you'll also need a sentence or two of your judgement at the end - whether overall you find the source convincing or unconvincing in relation to the question. If you want to shine, the judgement is the time to do it - if you know something about the historian you've been given, such as if they have a particular bias, or if they've taken a particular approach within the source which you can detect, bring it in as a final flourish for your judgement. The most important thing is to be confident in your argument; there's not much room for sitting on the fence with source questions, and the examiner would much prefer you to come to a strong conclusion of whether you find a source convincing or not than to hedge your bets.