If you have your sights set on working for a particular school, start with a well-crafted letter of inquiry to the school's principal, regardless of whether any jobs are currently posted. Because of shifting enrollment numbers and educators who decide to retire or move on last-minute, school principals don't always know they'll need educators until they need them urgently. Thus, it doesn't hurt to have your name filed away in that principal's mind, just in case.
Research the School
Your letter of inquiry should definitely explain why you'd make a good fit for the school, but it should also demonstrate that you know something about the challenges and needs of this particular school. Check out some of the district's recent job postings for jobs similar to the one you want, to get a sense of the skills and qualifications the district looks for in these positions. Also search for newspaper articles or district reports to find out as much as you can about the school. Reading district reports might reveal that students in the school have low reading scores, for example, while a recent newspaper article might inform you that the school just got funding for more chemistry equipment.
At the top of the page, write the principal's name, with his job title, the school name and its address on subsequent lines. Address the principal as "Dear Mr. X" or "Dear Dr. X," for example, instead of using a first name. In the first paragraph, get right to the point and tell the principal what position you're interested in. State that you know there are no open positions at the present time, but you'd like to be considered for any future openings.
Make your Case
In the next several paragraphs, use your research into required district qualifications for similar positions as well as your school-specific research to make your case as to why you'd be a good hire. If the school is struggling with reading scores, for example, talk about how you've recently completed a reading intervention course, or mention a specific technique you've used to improve a student's reading. You're going to include a copy of your resume with the letter, so there's no need to rehash that information. Instead, give more specific examples of how your education and experiences will help you meet the school's needs. Also mention you're willing to send along a copy of your teacher portfolio -- or better yet -- include a link to your online version.
It's appropriate to email your letter if the school's website or a direct phone call to the principal's office indicates it accepts queries or applications by email. In that case, include the title of the position you seek in the subject line, and paste your letter in the body of the email. Attach your resume as an Adobe PDF or a Microsoft Word document.
Proofread everything carefully whether sending by regular mail or email.
At the end of the letter, say you'll follow up with a call during a certain time frame, and then sign the letter "Cordially" or "Sincerely." Still, even letters written with impact won't always be enough to get your foot in the door, so look for other ways to get the principal to remember you. Get on the substitute teacher or para educator list in the school district and specifically request jobs at your target schools. Also try meeting the principal in other ways, such as attending volunteer events at the school or even volunteering to work in the school library or cafeteria, for example. Join the local teacher's association, where you'll get to network with many educators in the area. When a specific position opens up, you'll have more information to add to yet another cover letter, giving the principal even more reason to call you for an interview.