Your child should aim to achieve 80-90% in their weekly Bond/CGP book assessments. Any score lower than this would suggest they should possibly go to a lower book and work back up to that level.
If child is consistently getting over 90%, they may be ready to move up to the next book. However, it’s is important to still review the couple of mistakes that they did make in case there is a specific area they need to review in more detail before moving forward.