[Bertman]

In the past we have found that there have been a few options. 1. Miss the TAKS and go to the championship. In the past there has always been a make up date available for those students that do not take the test for one reason or another. The school will usually discourage that because it delays them getting there final scores somewhat. 2. miss the championship and take the TAKS. Pretty self explanatory. 3. Take a certified TAKS administrator with you as a chaperon, and make arrangements in advance for a conference room in your hotel so that the students affected can take the test there, missing some of the championship and still being able to do both. You can make a much stronger argument if all the students are passing all there classes. This will involve a lot of footwork well in advance, but it should be doable.
My best argument in the past has been (especially in Texas), if this was the school football team contending for a championship there would be no doubt that they would be not only permitted, but required to attend.
This is, of course, opinion based on past situation but there should be enough lead time to try to work it through.