Send the same day or the next morning after you notice something worth calling out. Specifics matter — a vague "great job" email does less than a sentence about what actually happened.
Hi {staff_first_name},
I wanted to take a minute to thank you for {specific_action — e.g., staying late on Tuesday to help with the parent conference, stepping in for {coworker} during the call-out, the way you handled {child}'s tough day}.
I know it might have felt like a small thing in the moment, but {acknowledgment_of_impact — e.g., it made a real difference for that family, it kept the whole afternoon from coming apart, it was exactly the kind of patience that child needed}.
You don't always get to see how much your work matters. I'm telling you now: it matters. Thank you.
{director_name}