There are reasons why schools have practice MSA tests. Let's begin with the "average" student in a general-ed classroom. The majority of students take the MSA test in their homeroom classroom, with their homeroom teacher. However, the classroom set-up, rules, and time constraints are very different than what students encounter on a daily basis. Desks are rearranged in rows, specific rules are in place regarding what kinds of questions test administrators may respond to, and these are timed tests. Everything is different, and the students need to be familiar with the changes in the physical arrangement in the classroom, as well as be familiar with test-taking strategies, and completing tasks within a specified timeframe. It's quite possible that your 3rd - 5th grade child may be asked to read a passage and respond to several multiple choice questions, as well as up to three "BCRs" (Brief Constructed Responses - which just means write out your answer in complete sentences and use text evidence to support your response) in let's say 30 minutes. That may sound like an easy task, but 8 - 10 year-olds have a harder time with concise written responses that include relevant text support. Practice sessions allow students the opportunity to experience a timed test, so that they can better learn how to manage their time. Additionally, teachers have the opportunity to see who is struggling with certain tasks, and can then provide meaningful feedback to students.
What many parents may not consider is the fact that there are many students who receive testing accommodations for a variety of reasons (student may have an IEP, 504 plan, ESOL student, RELL, etc.) These students leave their regular classroom, receive instructions from a testing administrator that they possibly have never worked with before, and likely will receive their individual accommodations from yet another adult in the building. So many teachers are involved in testing. Scheduling is impacted greatly, as so many staff members are involved during the testing window. Both students and adults need to become familiar with each other if they are paired together during testing. There is just so much involved, that "practicing" is essential so that the actual testing days run smoothly.