Here is a super quickie blog article. The 'quickiness' of this article should not allude to the notion that these 'thank yous' are an obligatory afterthought; rather, it's to emphasize that your child should not overthink this.
To reframe one point made above: the thank you should be genuine. The Admissions Officers—and if you've done a campus tour, then also the students, have taken time out of their very busy days to singularly devote their attention and time to your child and you. This alone should mean a lot.
Thank you notes have no bearing on an application; but they are generally good practice, and reinforce gratitude and maturity. For what it's worth, here are some points:
Timing
Within 48 hours (though in a couple of cases, my daughter ended up taking a few days).
E-mail or handwritten
I guess your call; but e-mail seems like more than sufficient (and more timely).
Structure
- Thank them for the time and conversation and/or tour
- Mention something specific that was discussed and/or share a reflection about the school or experience with the tour guide / Admissions Officer
- Close warmly
- And make sure the note comes from and is in your child's voice
For the record, I (as the parent) did not send thank you notes (I did not think my personal thank you worth enough to add to Admissions Officers' inbox noise).
And as a data point, I'd say about 20-30% of the students and Admissions Officers ended up responding with some type of warm acknowledgement of the note.