You can set a school wide event on SIMS by accessing the School diary on SIMS.
First Open SIMS and navigate to the top bar with the icons. You will see an orange book next to the flags, this is the diary. It is also highlighted below.
Once you are in the calendar, find the date you want to set an event for and right click. You will get the following options:
Select School Event for a school wide event.
DO NOT Select whole staff training unless it is a whole staff development day.
A new tab will appear and it will look like this:
Fill in the details of the event and select the appropriate category for the event. If this is an all day event, tick the ALL DAY EVENT box. If the event will occur between two times or across multiple dates, fill those options in instead. If you would like these events to duplicate then click recurrence and set the dates of recurrence.
Once you are done, click OK