What the results show on the report book are marks of a test or a series of them. If it is not up to your expectations, do not panic. What you can do is ask the teacher what topics or areas were tested, and in which sections your child has lost the most marks.
For example, in an English Language test, your child may have lost the most marks in composition writing, but may have done fairly well in grammar and vocabulary sections. Thus, then, only composition writing skills need to be worked on; do not jump to the conclusion that your child is "bad in English".