I have been faced with a similar situation my first few years of teaching. The solution my school system came up with was to test those students who enrolled prior to testing and to use their scores for placement purposes and data collection, however once a student enrolled after November their scores were no longer a reflection of the teacher and did not "count" when looking at class data as a whole.

I would not use these test scores as a basis for how you are teaching because you have not taught these students anything prior to the test. However, I would use the test scores as a way to determine where the students are in their learning and what they do and do not know.

This is always a tough situation especially when the students' results reflect on you. I would have to request that the students go into all day review for testing by using a review module on line. They would need to be supervised to make sure that they stay on course reviewing daily up until the test. The students would also have a study guide to review at home which includes checkpoint questions. The students can answer the questions and check their answers with the key in the back of the study guide.

Could you talk with your school and have them not start the student until testing is done?