Diagnostic and Placement Tests
A diagnostic test is designed to diagnose a particular aspect of a particular language. A diagnostic test in pronunciation might have the purpose of deter- mining which particular phonological features of the language pose difficulty for a learner. Prator's (1972) Diagnostic Passage, for example, is a short written passage that a student of English as a second language reads orally; the teacher or tester then examines a tape recording of that reading against a very detailed checklist of pronunciation errors. The checklist serves to diagnose certain problems in pronunciation. Some proficiency tests can serve as diagnostic tests by isolating and analyzing certain sets of items within the test. An achievement test on a particular module in a curriculum might include a number of items on modal auxiliaries; these particular items could serve to diagnose difficulty on modals.

Certain proficiency tests and diagnostic tests can act in the role of placement tests whose purpose is to place a student in a particular level or section of a language curriculum or school. A placement test typically includes a sampling of material to be covered in the curriculum (that is, it has content validity), and it thereby provides an indication of the point at which the student will find a level or class to be neither too easy nor too difficult but to be appropriately challenging.
Achievement Tests
An achievement test is related directly to classroom lessons, units, or even a total curriculum. Achievement tests are limited to particular material covered in a curriculum within a particular time frame.

Aptitude Tests
Finally, we need to consider the type of test that is given to a person prior to any exposure to the second language, a test that predicts a person's future success. A foreign language aptitude test is designed to measure a person's capacity or general ability to learn a foreign language and to be successful in that undertaking. Aptitude tests are considered to be independent of a particular foreign language, predicting success in the acquisition of any foreign language. Two standardized aptitude tests have been used in the United States - the Modern Language Aptitude Test (Carroll and Sapon 1958) and the Pimsleur Language Aptitude Battery (Pimsleur 1966). Both of these are English language tests and require students to perform such tasks as learning numbers, listening, detecting spelling clues and grammatical patterns, and memorizing.

While these two aptitude tests were once rather popular in the foreign language profession, few attempts have been made since then to experiment with new measures of language aptitude (see Parry and Child 1990). Two major issues account for this decline. First, even though the MLAT and the PLAB claimed to measure "language" aptitude, it appears that they simply reflected the general intelligence or academic ability of the student (see Skehan 1989a). At best, they measured ability to perform focused, analytical, field-independent, context-reduced activities that occupy a student in a traditional language classroom. They hardly even began to tap into the kinds of learning strategies and styles that recent research (Oxford 1990b, Ehrman 1990, for example) has shown to be crucial in the acquisition of communicative competence in con- text-embedded situations. As we have already noted in previous chapters, especially in Chapter Five, learners can be successful for a multitude of reasons, many of which are much more related to motivation and determination than to "native" abilities (Lett and O'Mara 1990).
Second, how is one to interpret a language aptitude test? Rarely does an institution have the luxury or freedom to test people before they take a foreign language to counsel certain people out of their decision to do so. So, an aptitude test biases both student and teacher. They are each led to believe that they will be successful or unsuccessful, depending on the aptitude test score, and a self-fulfilling prophecy occurs. It is better for teachers to be optimistic for students, and in the early stages of a student’s process of language learning, to monitor styles and strategies carefully, leading the student toward strategies that will aid in the process of learning and away from those blocking factors that will hinder the process.

The importance of these four different kinds of language tests lies in the fact that different tests serve different purposes. In order to select tests adequately and to interpret their results accurately, teachers need to be aware of the ultimate purpose of the testing context.
Within each category of test above there is a variety of different possible techniques and procedures. These range from objective to subjective techniques, open-ended to structured, multiple-choice to fill-in-the-blank, written to oral. Moreover, language has been viewed traditionally as consisting of four separate skills; therefore language tests have attempted to measure differential ability in speaking, listening, reading, and writing. It is not uncommon to be quite proficient in reading a foreign language but not in speaking, or of course for aural comprehension to outstrip speaking ability.

Beyond such considerations, tests of each of the modes of performance can be focused on a continuum of linguistic units, from smaller to larger:, phonology and orthography, words, sentences, and discourse. In interpreting a test it is important to note which linguistic units are being tested. Oral production tests can be tests of overall conversational fluency or pronunciation of a particular subset of phonology, and can take the form of imitation, structured responses, or free responses. Similarly, listening-comprehension tests can concentrate on a particular feature of language or on overall listening for general meaning. Tests of reading can cover the range of language units and can aim to test comprehension of long or short passages, single sentences, or even phrases and words. Writing tests can take on an open-ended form with free composition, or be structured to elicit anything from correct spelling to discourse-level competence.