It sounds like you have one Nano for several students and you want them to have their own boot drive instead of having their own full dev kit. Perhaps the following will clear up some confusion, although it isn’t an answer…
Is this an SD card model and not eMMC model? Answers to boot questions will change depending on model. Also, if this is not a dev kit (an SD card model plus dev kit carrier board), then other things change.
On the eMMC models there is QSPI memory which changes when you flash the Jetson. Those changes go beyond just creating a boot image. This also includes what are essentially pointers to devices for booting. The implication is that in an eMMC model, even if you boot “most” of it from an external media (e.g., USB thumb drive), there is no possibility of putting all boot content on the external device. The act of flashing such a Jetson changes the Jetson itself, and not just the boot media you see.
The SD card model of a Nano does have all of this content in the SD card (not sure how the SD card model would work if it has no SD card, but other boot media, e.g., just a USB thumb drive, never tried). Basically this means that all content on an SD card for use with an SD card dev kit can be cloned and different people could have different SD cards which are customized, e.g., different login names, different optional software, but eMMC models won’t have this flexibility.
See #50.
Consider that preexisting SD card images might not be the same as flashing once with JetPack/SDKM.
Also, note that it is good you are trying to use a true HDMI monitor, but it won’t do much good if first boot setup isn’t completed. I think you would still see HDMI output though, so no HDMI is some other issue. Anyone with that issue probably needs a full serial console boot log for each hardware change, e.g., when changing monitors and it still doesn’t work, then you’d still want a new boot log to see if the EDID is present (EDID is an i2c query of the monitor by the GPU using the DDC wire of the HDMI…and is mandatory for configuration to succeed, but it doesn’t mean the monitor is within available specs).
You should have a serial UART for serial console logging, and each student should know how to use this. The serial console is both the method of getting a definitive boot log, and also for seeing what goes wrong with video since it functions even when video and networking died. If you have a serial UART cable available for each student, then point them at this URL for how to use serial console:
https://www.jetsonhacks.com/2019/04/19/jetson-nano-serial-console/