The first is detailed source evidence and extra material, to support your argument. Let's use an example essay question here to demonstrate. In a history exam, the essay might ask: “To what extent was the character of Charles II responsible for his problems with parliament?".
The student is being asked to do two things here: to show an in-depth knowledge of Charles II's character, and to analyse which specific aspects of his character may have affected his political relationships.
Incorporating detailed evidence will always demonstrate how much you know of the subject matter, and will help to support the angle and strength of your argument.
The second element is linking to wider issues, topics or arguments that support your point of view. For example, in this particular history essay, a student could refer to other historical events that were responsible for problems between Charles II and parliament, but which were not related to his character.
Drawing on other factors in this way helps to increase the significance of your argument, and will round out your essay fully.
These two elements of analysis – including detailed evidence and linking to wider ideas – can be used to answer any 'To what extent...' question. In other words, when answering this type of essay question, keep the general structure the same and change the the appropriate information in the right places.
Remember also to analyse your evidence as you weave your argument. Do this by answering questions like, 'how significant is your evidence in supporting your argument?' and, 'what are the potential weaknesses that this evidence carries?'.
As with any successful essay, the question must be understood before an effective answer can be given. With a question that uses an "extent" in its stem, a case with evidence and analysis must be made. The idea of "To What Extent" is asking that the answer discuss how one element is greater in validity than others. The "To What Extent" question is asking that the student is able to make a claim about an assumption in a question and then place it in context and assess other conditions that surround the assumption. In the writing process, the student is making a definite claim whether it is to a "great extent" or "not a significant extent" that the assumption in the question is valid or verifiable. It requires the student to understand a specific context as well as the different conditions surrounding it in order to make a call to validity.
In answering a question that uses "To What Extent" as its stem, I think that the first part of the essay should focus on the assumption in the question. This will required support, elaboration and substantiation in making a particular case if something is valid to a great extent or not. Analysis and evidence would be critical here. The second part of the essay should focus on the role that other factors play in the question's assumption. Any question that uses "To What Extent" has to pull a topic that has other factors at play. For example, in the question, "To what extent can nationalism be seen as the primary cause of World War I," the understanding is that there were other causes to World War I and the critical element is to assert if Nationalism was the primary cause and how other causes would or would not be serve as the primary cause. The last part of the essay should reaffirm what the analysis and evidence presented has (hopefully) concluded. Put another way, is it to a great extent or not large extent that the assumption of the question can be seen? In crafting an essay with the "To What Extent" prompt, I think that this method becomes the most direct.