Dear [Teacher's Name],

I hope this letter finds you well. I wanted to take a moment to express my sincere gratitude for your unwavering support and inspiration throughout my academic journey. Your dedication to teaching and personal guidance has not only helped me excel academically but also shaped my character. I will always cherish the lessons you've imparted and the memories we've created. Thank you for being an exceptional teacher.

补充说明：

可以根据具体事例调整内容，例如提到某次作业的耐心辅导或考试前的鼓励。- 保持简洁明了，30词左右可包含核心感谢信息。