Write the introduction to your reaction paper. Introduce the book, article or video on brain development that you are writing about in the first sentence. Include the author and the date. Give a brief overview of the piece in roughly two to four sentences and end the introduction with your thesis statement.
Start the body with your reaction. If, for example, you read an article on the maturational theory of brain development and disagree with the conclusion of the author, state this and explain why. Write in the first person and use "I think" or "In my opinion" type statements.
Support your thesis statement on brain development throughout the body of your reaction paper. If you think that the attachment theory on which you watched a video is not a good option for most parents, then state why you feel that way. The body should be broken up into paragraphs that each contain one idea. The last sentence should transition into the next paragraph.
Conclude your paper with a brief restatement of your reaction on the specific brain development topic. Conclude with a summary of your overall reaction or a prediction of the effects. For example, if you agree with the author that a child should not watch television before the age of two, you can give a brief prediction on what you think would happen if she did. Do not introduce any new facts in the conclusion.