I am no expert but I would say that running out of time is the biggest factor in 'bright' kids not doing as well as expected. This is why I suggested a grounding in the basic types first. There is very little time on test day to read each question and then interpret exactly what is required. At the start of the VR process this is what predominantly slows the kids down. Without familiarisation it can lead to unfinished papers on the day, especially if they are having to wade through each question before even starting to answer it. Practice, and not having to read the question word for word, speeds the process considerably as I have noted with my two DSs over the last two years.
I remember back to when I started this VR journey. It took me 75 mins to complete one test! I like to consider myself reasonably articulate
but I found the codes impossible ("What the???"), the maths alright and some of the english subjective. For the kids, speed and accuracy is the key. In my opinion that is best achieved by familiarity, practicing and a solid grounding in the basics of maths and english (which some kids will have already). Definiately not too late!
Interesting Mitasol the research you refer to states
practice effects are greater for tests that have a time-limit compared to those without a time limit
PS..I can now do Walsh in about 35 mins
What a gal!!! lol
Perhaps what is most disturbing is that I actually timed myself...I must remember to get a life!