The type of thesis statement you need depends on the type of paper you are writing. Whether you are writing an informative or argumentative/persuasive paper, both of which are commonly required in twelfth grade, your thesis statement will succinctly state the over-arching theme of your paper, and it should appear as the final sentence of your introductory paragraph. Let's take a typical persuasive essay as an example. Think of a good thesis statement as having three parts: a concessions clause, a thesis, and a map (or sentence of division). In the concessions clause, you will acknowledge the opposing point of view; begin with the word although or while. For example, if you are arguing against school uniforms, your concessions clause would say:
Although many private schools and even some public schools require school uniforms,
The next part of your thesis statement is your thesis. This is the core point you are arguing for or against. Clues that will show you whether you are being persuasive rather than merely informative are words that show value judgments, such as should, should not, better, best, and unacceptable. For example, writing to oppose school uniforms, you would say:
students should not be required to wear uniforms to school
The last part of your thesis statement is a map that lists the three (or whatever number) main points you have in support of your argument. Sometimes this is called the because clause since it often starts with the word because.
because they stifle students' creativity, they make students feel like robots, and they don't prepare students for the real world.
Putting those three parts together, you have a complete thesis statement for a persuasive paper:
Although many private schools and even some public schools require school uniforms, students should not be required to wear uniforms to school because they stifle students' creativity, they make students feel like robots, and they don't prepare students for the real world.
The same format can be used for an informative paper; the thesis would be a statement regarding the main fact your paper will be explaining; the map would be three main parts of your subject.
Topic sentences should be general in nature and should introduce the subject that the paragraph will deal with. In our example persuasive essay about uniforms, you would have a topic sentence for each body paragraph that relates to the part of the map you are covering. For example, the first paragraph might say:
Schools should not require their students to wear uniforms because dressing the same as everyone else stifles a student's ability to be creative.
All the following sentences in that paragraph should revolve around the topic of student creativity and how uniforms inhibit it.
Your conclusion (final) paragraph should begin by restating your three-part thesis statement in slightly different wording. Summarize your key points, then leave the reader with a meaningful observation about why this issue is important. Following this format, your introduction, three body paragraphs, and conclusion will make a well-structured essay.
By the time you are a senior in high school, you should be able to write an essay according to whatever format is asked of you (i.e. persuasive, argumentative, narrative, compare/contrast, etc.). With that being said, the thesis statement can be, and usually is, included in the first paragraph. The introductory paragraph describes the issues that you will be discussing while also presenting your strong opinion in one sentence and written in 3rd person (Don't use "I" or "you"). Strong theses generally state that an issue should be addressed in a certain way without identifying yourself with a personal pronoun. Topic sentences are the main sentences presented in each following paragraph after the introduction. They can give you a focus of what to write about in each paragraph so you don't go off topic and discuss another issue at the same time. (This can confuse a reader.) Topic sentences guide the discussion of each paragraph, basically. For example, if the second paragraph will be about elephants, then don't start talking about tigers in that paragraph; save tigers for the third paragraph, instead. Remember, too, that the concluding paragraph can touch on all of the main points again as long as you drive home the main reason why you discussed them in the first place.