I think Bostonian was perhaps thinking of taking one of these early as being in itself practising, for taking it later to use for admissions purposes? But you've now explained that you have an immediate purpose for the score, so that doesn't really apply.
As for whether it's a good idea to practise before this instance - depends on all sorts of things, like your child's preferences, the score that would be useful and how confident you feel that your child will exceed it, how your child does with time pressure, etc. It's likely that a bit of practice would increase the score, but that doesn't mean it's necessary.
