Sure, here's a short yet heartfelt congratulatory message for a school's 35th anniversary:
Dear [School Name] Family,
Congratulations on reaching this remarkable milestone of 35 years! Your dedication to excellence in education has positively impacted countless lives. May the next 35 years be filled with even greater achievements and continued success. Happy Anniversary!
Warm regards,
[Your Name]
Feel free to personalize it further to better suit the tone and style you prefer.