In language teaching assessing is as important as teaching because only through assessment of and for learning is that teachers can move on their lessons.
The best way to conduct an assessment is by following three steps: a) pre-test or diagnosis, b) formative assessment FOR learning, c) final summative assessment of learning.
If your curriculum goes by standards, you should select at least 10-15 standards to cover per unit. It is best to write the standards into a checklist to ensure that you cover what you are supposed to.
The first thing that you do is the initial observation in the form of a pre-test where a task of each standard to be covered is included. The pre-test data helps you avoid wasting good teaching moments and get to what you really need to do. Check off the standards that the pre-test already covered and do not go over them except for enrichment activity. Always enter the pre-test data.
The second stage is the assessment FOR learning. This is a period where the student and the teacher work together in a number of tasks that are built to both teach and test, in a variety of instances, whether the standards that are being covered are also being learned properly. This type of assessment is often done with interviews, written and verbal tasks, and with activities that require more than one ways for the student to demonstrate mastery. This type of assessment should evidence the growth of the student. For this reason, it is best to keep a portfolio of the student works for record.
The final stage if required, is that the assessment OF learning is tested through a summative assessment in the form of a post-test. If you are measuring quantifiable gains in vocabulary, then the pre-test and the post test must be the same. This is the only way for you to be able to see growth.
Once again, verify that any summative assessment covers the standards that you used throughout the teaching, and only what was covered throughout the unit. The data will show you now the before-during-after effect of your teaching intervention, hence helping you make sure that you tested exactly what needed to be assessed.