OP, get hold of the markscheme for the exam board, they are easily available online. You will see that marks are weighted in favour of analysis, over knowledge. This means your son needs to have good subject knowledge first, in order to apply analytical skills, like evaluating sources and making judgements on historians’ interpretations. This will also include identifying causation, change, turning points, significance.
Content is taught in class. Your son will need to have a knowledge of the chronology of each topic and to understand each topic in detail. This knowledge supports his analysis in his essays. The GCSE spec has a lot of content to learn. Analytical skills and how to answer questions are also covered in class as a matter of routine. Homework etc. Will support that learning of both content and skills.
If your son doesn’t have even the basic knowledge, then he cannot revise it. You say you want revision, but what your son needs to do is learn it first. Teaching and learning are a 2 way street. The teacher facilitates the learning, but it is your son’s responsibility to commit to that learning. Then you can move onto revision. Flash cards etc.
You don’t have long to construct an essay in the exam, so right now, with mocks coming up, your son should have knowledge already embedded to call upon in the exam, so that can apply his (mastered) analytical skills. This is dependent on learner commitment.
All of this is hard work and the students that receive the best marks are the ones who commit to the course from the beginning and responds to the feedback his teacher gives on his responses to practice questions.
At this stage, your tutor will be thinking about how your son applies his skills using his existing knowledge. He can then help your son to master those skills. Without the knowledge, your son is, essentially, starting from scratch. So revising something that isn’t already there, isn’t going to work. If your son isn’t activating his cognitive skills in class, by making notes and responding to feedback, then he isn’t learning. Therefore, he cannot revise.
Students are taught revision techniques in all subjects. The techniques are the same. Every subject does mind maps.
Most schools will still be covering content and asking students to apply what they have learned to practice questions, feedback is offered and students should respond to the feedback in order to improve.
At A level, these skills are used on content that is more complex with a requirement to write essays in a greater level of analytical detail, not just in exams, but also coursework where students are asked to evaluate a number of historians’ interpretations of an enquiry.
Your tutor knows the spec back to front and knows what is required to achieve each grade level. Listen to him, you’re paying for that expertise. Bluntly, and with no wish to cause offence, you’re not the expert here.