• Speak to your child's teachers. Get your child to speak to the teacher(s) of the subject(s) with the low result(s). Get a copy of the paper(s) and go through it/them with the teacher(s). Was it a timing issue? Did the result highlight gaps in understanding? Had your child failed to prepare?
• Attend extra sessions. All faculties provide extra sessions - they come in the form of after school lectures, lunch clubs, 1:1 sessions - encourage your child to take part in these opportunities. 
• Speak to another teacher in the faculty. If your child does not understand how Mr X explains something, suggest he speaks with Mrs Y. A different approach might make all the difference.
• Retake papers and questions, resubmit work. The teachers will be more than happy to mark and go through additional work your child is wanting to put in. They are willing to put in as much effort as your child does - if your child has had another stab at a question, the teacher will re-mark and give more feedback. There seems to be an endless amount of support by Deer Park teachers!
• Prioritise. If your child got a low grade in a core subject or one they want to pursue at A Level, they could choose to prioritise their revision for that subject. Could they sit a Foundation paper in another subject? Speak with all teachers concerned, they really do have your child’s best interest at heart.
• Tutoring. If this is something you decide to do, in addition to all of the above, then speak to the teachers, as they will be able to give specific advice on areas your child needs.

Finally, be kind to your child. They are under an enormous amount of pressure and they need you on their side. Let them off chores, spend time with them doing something other than school work. Ask how you can help them - it is often in the strangest of ways.

Do not give up - in my experience it is possible to go up 6 grades between mocks and results day!