If those reading your resume get lost or bogged down trying to understand it, they are likely to move on and pick up another resume. In other words, your resume should not be an autobiography. Don't duplicate information that will be in your transcript. And save information on your ambitions, long-range plans and ultimate goals for the interview where you will have a chance to detail your strengths and attributes in person. Remember, space on your resume is valuable, and you should only include those items school administrators will need to gauge your abilities and skills as a professional teacher.
Nothing says more to an employer than typographical errors and poor grammar.
Your resume is an example of your writing ability, and if it has errors, you are sending a bad message to an employer. They may assume that your work, like your resume, tends to be careless and needs to be checked constantly. But, remember, the final product is your responsibility. If you do all this and take the editing and proofreading seriously, you will have a final product that presents a great impression. When finalizing your resume, use an attractive layout with ample margins.