Innumerable classroom events enable teachers to gather information about pupils by observing, questioning, listening to informal discussions and reviewing written work. In formative assessment this information may be used immediately to help pupils or it may be stored and used to plan future learning opportunities. The information gathered in this way is often inconclusive and may be contradictory, for what pupils can do is known to be influenced by the particular context. This creates a problem for summative assessment but is useful for formative purposes. Serving the two purposes requires a distinction to be made between the evidence and the interpretation of the evidence.