Your conclusions very important and must be detailed, but clear and not waffle! Any calculations which you do not mention are considered irrelevant data. Make statements and comparisons from your calculations across year groups and gender and link these to your original hypotheses. (More info in Your Report section of this booklet)
You must consider how reliable your findings are. Can you use them to make correct predictions for the whole school? Could they be used to make predictions for your school?
One way of considering the limitations of your sample is to compare the key results in your summary table to calculations for the whole population (use Excel to obtain these calculations)