Write your abstract and report before beginning the conclusion section. An abstract is a brief summary of the report, usually one to two paragraphs, that goes before the introduction. A lab report also includes an introduction, methods, result and discussion section. The summary is part of the conclusions section at the end of the report.
Read your introduction to find out if you answered the scientific question you were asking by doing the experiment in your lab. Write down whether the lab answered this question or not. Determine whether you met the objectives set forth in your introduction section by doing the lab. Write this information down as well. You will use this information when writing your conclusions section.
Write your conclusions section. Begin with a brief summary of the purpose of the lab and any results that you found. Do not present any new ideas. The summary and conclusions section is written to finalize the lab report without raising any new questions.
Write how the results compared with what you predicted initially. If you predicted something different than the results, analyze why this occurred. Write what your findings mean to the scientific world and whether you consider the experiment to be successful or not. Keep your conclusions section to one or two paragraphs only.