When DS did his practice test, he did it section by section rather than all at once. I think he did one section on Saturday, one on Sunday and then the other two the next weekend. Yes, the ACT takes stamina and if you are "practicing" building stamina it makes sense to take it all at once. But if you want to know what your child can do, then taking each section fresh is probably more helpful. And breaking it up was the only way that would fit into our schedule!