The fact that practice is necessary at all indicates the expectation of error. However, in school we often turn what ought to be practice into a test. The math teacher, for example, assigns problems to be done for practice but then takes a grade on the paper. The science teacher sends students into the laboratory so they can practice scientific procedures and then grades lab reports on the basis of whether or not students obtained the predicted results. Similarly, we assign a composition task and then grade the papers.
Every paper becomes, in effect, a test.
Yes, students demand grades on papers and they often do not do the work if no grade is given, but this is a situation that we educators have created, and it is a situation we can change if we decide to do so. When we step back from the situation, we may be able to see that audience response is really the most effective. Receiving a letter from a pen pal or a company, hearing the audience applaud at the end of a student written play, reading an editorial written in reaction to one a student submitted, being notified that one's poem or short story will be published in a magazine - these are the forms of evaluation that matter the most. These are the responses that motivate students to continue writing or improve their work. Thus, it is important to consider that effective assessment also hinges on the types of tasks in which students engage.