It depends. (Typical psych response.
)
On the one hand, very young children are not easy to test, which suggests that low estimates are likely. On the other hand, the difference between a highly enriched environment and an intellectually impoverished one has more impact on the performance of young children, which may result in low estimates for under stimulated children, and high estimates for those from unusually enriched environments. (Remember that norms are developed based on representative samplings, which will include some low, some high stimulation, and mostly average stimulation. So typical experience, not optimal.)
Small children are also notable for a rapid and uneven pace of development for the entire age group, across ability levels. This makes performance at one moment in time difficult to compare reliably with age peers, as the range of possible development for any one ability level is quite wide. That range also overlaps with possible development for quite a diverse range of adjacent ability levels, so that one absolute result may be attached to any one of a a huge range of possible meanings.
Anecdotally, I have definitely seen above average preschool scores move in both directions. As a statistical generalization, one would expect extremely high scores to be more likely to decrease, extremely low scores to increase, and average scores to change the least, due to regression to the mean.
Sorry that this does not really answer the question of too high or too low for your child! There are too many variables.
