INTRODUCTION
In the educational psychology, one of the basic themes is the realization that nobody in this world is exactly like somebody else. Individual differences are notable in differences in performance at school .These are intra-individual variables which reflect differences in an individual’s abilities from one situation to another ,for example ,between numerical ,reading ,sporting abilities and inter-individual variables which reflect differences between individuals at any given point in time .Individual differences which are related to academic achievement that may affect performance may include age ,cognitive style ,home background ,ability to remember given information ,level of confidence and amount of previous learning experiences. In order to identify these pupils, assessment tests of both scholastic aptitude and achievement are used to assess pupil variability. This discussion focuses on the role of criterion referenced tests and norm referenced tests in the teaching and learning process.

Definition of key terms
Criterion referenced test
According to Popham and Hesek (1969),a criterion referenced test is a measure used to identify an individual’s status with respect to an established standard of performance .Similarly ,Mpofu E (1991),says a criterion referenced test measures whether a student has or has not reached the criterion or specific level of achievement .This means that criterion referencing as the name implies ,involves determining a student ‘s grade by comparing his or her achievements with clearly started criteria for learning outcomes and clearly stated standards for particular levels of performance. The major focus is on how pupils’ skills and abilities are measured and tested in the classroom.
Norm Referenced test Popham and Husek (1969), define a norm –referenced test as a measure used to identify an individual’s performance of others in the same measure .Glaser (1963), defines norm –referenced tests as measures of students ’performances against the scores achieved by others completing the same test. These definitions lead us to focus on the ability of norm referenced tests to be useful for classification, selection and making decisions as to how much a student has learnt in comparison to others.

BODY
Criterion referenced test can be used to evaluate individualized learning programmes , diagnosing student difficulties ,estimating student abilities in a particular area ,measuring what a student has learned ,certification of competency ,controlling entry to successive units of construction and selection. Such test scores depend upon the specifying of an absolute standard of quality .This standard is independent of scores achieved by other students attempting the same test and completing the same course. Criterion referencing is worth aspiring towards .Criterion referencing requires giving thought to expected learning outcomes ,therefore, it is transparent for students ,and the grades derived should be defensible in reasonably objective terms .Though criterion referenced tests, students are able to trace their grades to the specifics of their performance on set tasks.
Criterion referencing lays an important framework for student engagement with learning process and its outcomes. Recognizing, however, that some degree of subjectivity is inevitable in higher education, it also worthwhile to monitor the grade distribution, that is ,to use a modest process of norm-referencing to watch outcomes of a pre-dominantly criterion-referencing grading model. In doing so, if it is believed too many students are receiving high grades, or the distribution is some way oddly spread, then this might suggest something is amiss and the assessment process needs looking at. There may be , for instance, a problem with the overall degree of difficulty of the assessment tasks for example, not enough challenging examination questions , or too few or assignment tasks that fail to discriminate between students with differing levels of knowledge and skills. There might also be inconsistencies in the way f different assessors are judging student’s work.
Leo M. Schell (1981), views the essential characteristic of norm referencing as that students are awarded their grades on the basis of their ranking within a particular cohort. Norm referencing involves fitting a ranked list of students ‘raw-scores ’to pre-determined distribution for awarding grades. Usually, grades are spread to fit a’ bell curve’ or a’ normal distribution curve’, either by quantitative, informal rough –reckoning or by statistical techniques of varying complexity. For large students’ cohorts, such as in senior secondary education, statistical moderation processes are used to adjust or standardize students scores to fit a normal distribution .This adjustment is necessary when comparability to scores across different subjects is required, such as when subject scores are added to create an aggregate ENTER score for making university selection decisions.
Norm referencing is based on the assumption that roughly similar range of human performance can be expected for any student or group .There is a strong culture of norm referencing in higher education .It is evident in many common place practices, such s the expectation that the mean of a cohort‘s results should be a fixed percentage year in ,year out. It can also be seen when first class honors is awarded sparingly to a set number of students .In contrast ,criterion referencing has no pre-determined grade distribution to be generated and a student’s grades is in no way influenced by the performance of others. Theoretically, all students within a particular cohort could receive very high or very low grades depending solely on the levels of individual’s performances against the established criterion and standard. Thus, the goal of criterion referencing is to report student achievement against objective or reference points that are independent of the cohort being assessed.
Raymond Sumner and T.Robertson (1977), discovered that criterion referencing can lead to simple pass-fail grading schema, such as in determining fitness to practice in professional fields. Criterion referencing can lead to reporting student achievement or progress on a series of key criteria rather than as a single grade or percentage .Logically ,norm referencing must rely on some initial criterion -referencing can lead to reporting student achievement or progress on a single grade or percentage .Logically ,norm –referencing must v rely on some initial criterion –referencing ,since students ’’ raw’ scores must presumably be determined in the first instance by assessors who have some objective criteria in mind . Criterion referencing, on the other hand, appears more educationally defensible but it may be very difficult, if not impossible, to implement in a pure form in many disciplines. It is not always possible to be entirely objective and to comprehensively articulate criteria for learning outcomes .Some subjectivity in setting and interpreting levels of achievement is inevitable in higher education. This being the case, sometimes the best we can hope for is to compare individuals’ achievements relative to their peers.
Norm referencing on its own, if strictly and narrowly implemented, is undoubtedly unfair. With norm referencing, a student’s grade depends, not only on his or her level of achievement, but also on the achievement of other students. This might lead to obvious inequalities if applied without thought to any other considerations, for example, a student who fails in one year may well have passed in other years. The potential for unfairness of this kind is most likely in smaller student cohorts, where norm referencing may force a spread of grades and exaggerate differences in achievement. Alternatively, norm referencing might artificially compress the range of difference that actually exists.
Linn Gronlund (2000) regards a criterion referenced test as “a test or other type of assessment designed to provide a measure of performance that is interpretable in terms of a clearly defined or delimited domain of learning tasks”. The goal of a criterion referenced test is to obtain a description of the specific knowledge and skills each student can demonstrate. This information is useful for planning both group and individual instruction. Criterion referenced tests can be scored in the way of checklists, rating scales, grades, rubrics and percent accurate. This matches Mpofu. E (1991) observation that a criterion referenced test is one that provides for translating test scores into a statement about the behavior to be expected of a person with that score or their relationship to a specified subject matter. The objective is simply to see whether the student has learned the material.
The criterion is the domain of subject matter that the test is designed to assess, for instance, “students should be able to calculate the mean temperature for a given weather station” and the cut score maybe that students should correctly answer a minimum of 80 percent of the questions to pass. However, a number of criticisms have been leveled against criterion referencing. Some scholars say criterion referencing tells us what a student knows or can do, but not the degree of excellence or deficiency of the student’s performance in relation to peers. Some say it is unrealistic to expect teachers to provide the degree of detail necessary in writing instructional objectives for good and reliable criterion reference measures to be obtained. Moreover, knowledge and understanding do not lend themselves to clear definition and, hence, it is extremely difficult to establish adequate criterion for achievement. Criterion referencing measures discourage the use of problem solving questions and instead, encourage right and wrong solutions, with a tendency towards teachers determining various answers while student is constrained to choose from the teacher’s selection.
Tests constructed to provide norm referencing will not adequately sample the course objectives. A final grade received by a student in any one subject conceals the student’s misunderstandings, inadequate study skills and potential limitations in that subject. To have meaning for such interpretation, any individual’s score needs to be related to the content of the test. Over a period of time, some students who are continually exposed to norm reference tests will suffer diminishing level of motivation. This is because any given mark does not signify a definite amount of knowledge, and hence has little relevance for content or absolute framework reference. Black and Dockwell (1980) noted that most cases where formative or continuous assessment took place, feedback was in the form of general attainment grade or real and no real information about specific strengths and weaknesses. Furthermore, assessment took place at the end of each unit of work by which time it was too late to take remedial action. Therefore , if students are helped when and where they have learning difficulties, given sufficient time to achieve mastery, and there is some clear criterion of what constitutes mastery, a high level of learning will be achieved (Bloom, 1976).

Conclusion
Both criterion reference test and norm reference tests are essential components of teaching strategies. There is need for feedback of information to students as to their progress thus making each test part of a learning experience. In my own point of view, best practice in grading in education involves striking balance between criterion referencing and norm referencing. This balance should be strongly oriented towards criterion referencing as the primary and dominant principle.

References
Black and Dockrell (1980) Diagnostic Assessment in Secondary Schools. Scottish Council for Research in Education.
Bloom, B.S (1976) Handbook on Formative and Summative Evaluation of Student Learning. McGraw-Hill.43-60. New York.
Glaser,R (1963) Instructional Technology and Measurements of Learning Outcomes, American Psychologist,Vol.18:519-521
Linn, R.L and Gronhund, N.E (2000) Measurement and Assessment in Teaching (8th ed) Upper Saddle River, NJ: Prentice Hall
Mpofu, E (1991) Testing for Teaching. Harare: Longman
Popham, W.J and Husek, T.R (1969) Implications of Criterion Referenced Measurement. Journal of Educational Management. Wiley.
Robertson, T.S and Sumner, R (1977) Criterion Referenced Measurement and Criterion Referenced Tests. NFER Publishing Co.
Schell, L.M (1981) Diagnostic and Criterion Referenced Reading Tests: Review and Evaluation, IRA. The University of Michigan.