First, you must formally resign from your teaching position. What do you write in a teacher Retirement Letter?In addition, you must wait 30 days from the effective date of your resignation before performing any post-retirement teaching for the same employer. When leaving the university, you must submit a letter of resignation to your manager and HR providing your last day of work. In the body of the letter, state your intended retirement date (your last day) and your thoughts on a transition plan. How much do teachers make Illinois CPS? The reason for this is your pension and group insurance begin with SERS on the first of the month following your resignation. The Illinois General Assembly created the Teachers' Retirement System of the State of Illinois (TRS) in. Once the form is filled out, please print it (sign the form if necessary) and mail to SERS. A retirement letter is a type of resignation letter, but the main difference is its purpose.