How to react to some students who book an appointment and do not show up? I wonder what is the best strategy to follow to respond to students who book an appointment with you and do not show up. It is just so un-nice when this happens.
I do not want the student to be upset but at the same time to honour his/her bookings.
Back when this was something I had to deal with, I would:

Always have something to do if someone doesn't show up for their appointment, or if their question gets resolved very quickly.

Write brief emails to no-shows along the lines of



Dear X:
I'm following up on our appointment today at 14:00. I hope everything is OK with you.
Let me know if your question is still relevant and you would like to reschedule.
If you answered your own question, I'm glad, but next time I'd appreciate
a heads up for scheduling purposes. Ditto if something came up and you just couldn't
make it. See you in class tomorrow, I hope!


Get progressively more direct if people missed several appointments, to the extent of refusing to make further appointments (leaving the student the option to come for the office hour I had for appointment-free visits every week).

Note the tone of the email in point 2 is not demanding of an explanation (or indicating a desire to judge whether excuses provided are adequate), but is also openly asking for a change in behaviour, without pulling rank or going passive-aggressive. Generally I got belated apologies and improved future behaviour. And a couple of times the &quot;I hope everything is OK&quot;, meant genuinely, surfaced that something pretty dire had happened (where a pure chastising email soliciting an apology would have been cringingly tone-deaf!), including a student on the verge of an emotional breakdown where we were able to get them help.
Now, a couple of decades later, I'd still do the same -- and suspect I've written stuff not too dissimilar in tone to peers and superiors too!
Basically: be frank about what you need to change, don't make an investigation of it, and open the door to empathy.
Editing to add: Comments/other answers have pointed out potential different cultural expectations, and/or that the tone is not optimal if there turns out to have been a real emergency. Regarding the first, agreed: needs to be tempered by cultural norms. But if student behaviour feels outside of local norms, do go ahead and address it. Regarding the 2nd, also true. At the risk of going very math/stats-nerdy, there is a Bayesian prior regarding what caused the missed appointment. My answer assumes the Bayesian prior is fairly flat between emergency, forgetfulness, student self-absorbtion/failure to consider from others' point of view, and overall excessive academic stress. The tone tries to be acceptable and hopefully effective in all these instances. If your Bayesian prior is more heavily weighted to one pole, your optimal tone will change. This includes repeat offenders (where the Bayesian prior weighs more heavily on self-absorbtion), reason to suspect emergencies, etc.