1 TEST THE ABILITIES WHOSE DEVELOPMENT YOU WANT TO ENCOURAGE
For example, if you want to encourage oral ability, then test oral ability. This is very obvious, a straightforward matter of content validity, yet it is surprising how often it is not done. There is a tendency to test what it is easiest to test rather than what it is most important to test. Reasons advanced for not testing particular abilities may take many forms. It is often said, for instance, that sufficiently high reliability cannot be obtained when a form of testing (such as an oral interview) requires subjective scoring.
2 SAMPLE WIDELY AND UNPREDICTABLY
Normally a test can measure only a sample of everything included in the specifications. It is important that the sample taken should represent as far as possible the full scope of what is specified. If not, if the sample is taken from a restricted area of that specifications, then the backwash effect will tend to be felt only in that area. The new TOEFL writing test will set only two kinds of tasks: compare/ contrast; describe/interpret chart or graph. The likely outcome is that much preparation for the test will be limited to those two types of task. The backwash effect may not be as beneficial as it might have been had a wider range of tasks been used.
3 USE DIRECT TESTING
Direct testing implies the testing of performance skills, with texts and tasks as authentic as possible. If we test directly the skills that we are interested in fostering, then practice for the test represents practice in those skills. If we want people to learn to write compositions, we should get them to write compositions in the test. If a course objective is that students should be able to read scientific articles, then we should get them to do that in the test. Immediately we begin to test indirectly, we are removing an incentive for students to practice in the way that we want them to.