In the case of the OP's child, the lack of scantron experience would probably be the place to start.
This raises a good point. One tricky thing about computer-read forms... within each section, some are numbered horizontally (across in rows) while other computer-read forms may be numbered vertically (downward in columns). Therefore it can be easy to mismark if one is focused on the questions and not being mindful about the answer sheet. Stray marks and incomplete erasures can also be problematic.
