If you've been in the classroom 30 years it can be tough to get that retirement letter down on paper, especially if you feel compelled to encapsulate your entire career on one sheet of paper. Keep in mind your audience: your retirement letter may be read aloud at a faculty meeting, sent on to the board of education, and, in some cases, it may even be published in a school district publication.
Set the Appropriate Tone
Professional while friendly is the tone to strive for in a teacher retirement letter. Achieve this tone by leaving out words you wouldn't actually use in ordinary conversation and adopting a relaxed, conversational, manner. At the same time it's important to remain professional; think of the tone you would use in interviewing for a job. A touch of humour, however, is appropriate.
A one-page letter is a suitable length for a retirement letter. With all the memories, all the experiences---good and bad, all the funny and poignant stories, any retiring teacher would have enough material for a book. However, a retirement letter needs to be concise; the letter needs to announce the date at which the retirement will be effective, make acknowledgments where appropriate, and, optionally, include a brief overview of one's teaching career in the school or district.
It is certainly appropriate to include those to whom you would like to express thanks in your retirement letter. When doing so, be specific in just what it is you have appreciated. For example, "I would like to thank Principal Wilson for his constant support of the theatre program here at Nelson High; he came up with needed funds, encouraged kids to audition for shows, and he showed up at every performance."
As tempting as it is to talk about what you would like so see done differently in the school, avoid the temptation to turn your retirement letter into a list of the changes you would like to see happen. Because you are no longer going to be in a position to affect any changes, it is really not appropriate for you to suggest them. "If only . . ." (If only class sizes had been smaller, for example) statements will only detract from what could otherwise be a tranquil retirement message.
Keep the Door Open
In the months or years following retirement, teachers sometimes decide to return to teaching, substitute teach, or take positions as mentors or consultants for the district in which they taught. You might consider including in your retirement letter a statement such as "Perhaps our paths will cross again in the future; for one thing, I know I'll be buying tickets for the faculty pie toss at next year's carnival."