Hi NightShade41,
welcome to the Apple (user-to-user) Community.
Re: Allowing Siri response to stay on screen longer
Am no expert in this area, yet your post surely deserves some response.
I do not know of any setting that would allow more time for spelling responses to stay on screen.
(Am wondering if the iPhone SE is the device your son uses.)
If appropriate:
Your child could ask to see a particular word on screen another way Eg: "Hey Siri, Look up rhubarb" or "Show me rhubarb in a dictionary" to see what Siri finds on the web, and may put on the screen until he dismisses it.
or
It may help to hear Siri spell the word aloud instead of seeing it on screen, so your child can focus on his writing work instead of the time used in looking back and forth at the screen.
The article below is for iOS 17: if needed, you can change the iOS version at the top for accuracy.
If you haven't already:
You may want to look through : Change Siri accessibility settings on iPhone - Apple Support or
Change Siri accessibility settings on iPad - Apple Support to see whether there is a workable solution for you both.
Another option is to ask Siri to spell that word again, after it disappears.
Siri can learn from what happens, and what is requested / needed, so after a few repeats, Siri may make some adjustment.
_________________
If you still need help with this issue:
You may want to reach out by phone / online chat / email to Apple's Accessibility Support:
(NB: You can "Get Support" from the link at the bottom of their website:)
Accessibility Support - Official Apple Support
or
You can send feedback (or a feature request) to reach those who work behind-the-scenes at Apple. They will likely not reply, and it won't solve things immediately, yet your feedback will be considered by those who can make changes. If others also need more Siri control with this issue, we may see it addressed in an update.
Feedback webpage: Product Feedback - Apple
All the best :-)