There are many possible interpretations of intrasubtest scatter. Sometimes it reflects intermittent attention or motivation. It could be an artifact of how high he went and how divergent his exposure has been from that of the norm group; where he probably absorbed knowledge on his own, not through conventional instructional experiences, there may be differences in his repertoire compared to the conventional gradation of item difficulty.
What it usually means to me is that the results are a probable low estimate of ability. He is at the very beginning of his formal education. If there are idiosyncratic gaps, they will likely fill in as he receives (one hopes) appropriate instruction. If the above speculation is correct, a retest in two or three years will probably result in higher scores. If the scatter is from something else, like intermittent attention, then addressing the deficits in sustained attention or impulsivity will probably also raise scores on future retests.
I have also had examinees with scatter that appeared to reflect changes in problem-solving strategies as tasks became more challenging. In those cases, simpler methods were used for simpler items, until they began failing, at which point more sophisticated strategies were called into use, but not before a few incorrect responses had been recorded. In order to know if this was the case, the examiner would most likely have had to do some additional inquiry or testing of limits.
A similar situation is when the examinee is slow to pick up the task expectations during the first few items, or at a transition in task complexity. Some very bright children who have executive function deficits will generate this type of pattern, due to weaknesses in the EF known as shift, or flexibility.
