Approached creatively, source analysis can be both a stimulating and enlightening exercise at key stage 4 and above. Tackling sources not only encourages students to show off their background knowledge, but develops their understanding. Yet even though sources are the stuff of history, for many students - and, dare I say it, teachers - they are approached with a sense of resigned duty rather than genuine interest. All too often, "source work" is a phrase in which the second word is the operative one, with practice exam questions about reliability and usefulness tackled with glum, even confused, determination.

Part of the problem lies in the fact that students are expected to provide distinct answers about what a source tells us, how much it tells us, how useful it is and how reliable it is - even though for the intelligent layperson there is infuriatingly little difference between such questions.

With these problems in mind, I use the diagram (bottom right) with my students to illustrate that although these questions are closely related they are still distinct.

The usefulness of a source is assessed as a combination of how much information is in it and how reliable that information is. The most useful sources are those we can trust and that tell us a great deal; the least useful are those that tell us very little and whose reliability is questionable.

With that matter cleared up, students are now in a position to focus on the demands of specific questions.

"Comprehension in context" is the key to answering the question "How much does it tell us?" In other words, background knowledge needs to be deployed in every sentence to answer the question effectively. Considering what the source tells us, for example, involves explaining what it means - not describing what it says.

Rather than merely summarising or describing the extract: "It tells us that 20,000 British soldiers were killed in the Battle of the Somme," students should instead use their background knowledge to elaborate on and make deductions from the source: "...which helps explain why so many people were later determined that this should be 'the war to end all wars'."

Similarly, pointing out gaps in the source: "It does not tell us the objectives of this battle," is nowhere near as effective as filling these gaps in from background knowledge: "... - for example, to divert German troops away from Verdun".

To illustrate the point, get students to ask how much a particular source tells them about a topic they have never studied. However intelligent their response, it will never deserve a high mark because it will be clear that the student doesn't know enough about the topic to place the source in its full context.

To produce a balanced assessment of usefulness, the amount of information given by any source must be weighed against how reliable it is. All too often, students lazily equate primary sources with reliability and secondary sources with unreliability. But teachers should impress on students that this is not only unhelpful, but plain wrong in many cases: primary sources are so wrapped up in the events they describe that they cannot see the wood for the trees, while secondary writers benefit from objectivity, perspective and scholarly analysis. Every source must be considered on its own merits, and to this end I encourage students to think in terms of the mnemonic PACT: Purpose: every source is produced for a reason. Was this to inform and educate, or to persuade, frighten or even mislead? Photographs provide particularly fruitful avenues of enquiry here, if students can avoid the mantra that "this is a photograph, so it could be staged". If students are going to make such statements, they need to draw on evidence to substantiate the assertion.

For example, encourage students to tell you how many people are clearly present in the picture. It is rare that the class will include the photographer himself in their count, yet his presence often tells us a lot about the reliability of the source: if this is a genuine depiction of three Freikorps soldiers firing on communists, would a photographer really be standing in the middle of the battle zone with his tripod and Box Brownie?

Author: just as all sources have a purpose, so too do they all have a producer. Occasionally students will know something about the particular author - Churchill delivering the iron curtain speech; Kennedy commenting on the Cuban missile crisis - in which case the key question to ask is "are they saying exactly what we would expect them to do in this situation?"

If they don't - in other words, they are not speaking with self-interest at the forefront of their minds then this suggests that the source is more reliable than it otherwise would have been.

Context: does background knowledge substantiate what is being stated in the source? Whether it does or doesn't, students should not simply assert this point: "This source says that life on the Western Front was horrible, and I know from background knowledge that this is true" but give specific examples to illustrate the fact. For example, "The Tommies were infested with lice and had to share their dugouts with rats the size of rabbits."

Tone: a final clue to the reliability of a particular source is the tone in which it is written. A source which is vitriolic, sarcastic, embittered or dramatic is one which lacks the proper perspective and which should therefore be handled with care. Nevertheless, if a source is unreliable, this does not mean it is useless: factually unreliable sources give us a great insight into the opinions and attitudes of people in history. Indeed, in many instances - Keynes's diatribes against Versailles, or Churchill's iron curtain speech, for example - such sources profoundly change the course of history even as they comment on it.

PASS THE SOURCE

Primary source: a source written at the time or by someone who was at the events they describe.

Secondary source: a source written later or by someone who was not there at the time.

Sources can be both primary and secondary. Primary in the sense that someone may have been there, but secondary in that they are recalling them 50 years later; primary in that they were written at the time, but secondary in that the person recording them was not there.