Too Much Testing

Testing is a fact of every student's academic life. However, at schools labeled as needs improvement or failing, testing seems to be done excessively. At my clinic placement, my third graders have been practicing for the CMTs by taking practice tests every Wednesday. In the beginning the students did not think much of it, but now that it has become a regular part of their weekly routine, they dread the thought of it. As a result, the students mark down anything just to say they are done with the test and some students become so frustrated that they do not do anything.
So my issue is that I do not understand how the school district justifies preparing for a state test by making students take frequent practice tests. I think this is an ineffective way to prepare for an assessment. I also think the results received from the practice tests are invalid measures of the students' actual performance, since many of the students either refused to do the test or marked any answer. I understand that they want to use the practice tests as a means to inform instruction before the real test occurs, but if the test results are not reliable then the instruction created will not be the most useful.
Rather, I think a better way to prepare for the test would be to teach the particular skills and objectives assessed on the test and then follow it up by giving students the opportunity to see practice that portion of the standardized test. By doing it this way, the practice test is done with a clear purpose in the students' and teachers' minds, the students are not overwhelmed by the test, the results are more valid and will help better inform instruction.