Our children did the sample test over a couple of Saturdays. Two ACT sections at each sitting, with the actual timing. Our results were consistent with the actual test results. (One child was 11, we did the test to see "where is he really?"; the other was a HS junior who was taking the test for college apps). Our choice of taking the ACT was tied to a few factors: we were in an ACT state, the ACT was given at our HS so we felt the younger one would be more comfortable in a familiar environment, the SAT test sites were not convenient, and (bad parenting, I know) we wanted a comparison score.
Be sure that you both correct the test, and have them look up the answer explanations for ones they struggled over or got incorrect. When one of ours took the SAT later, he found an error in the Kaplan prep book he practiced the test from.
