I’ve done this on ocassion to help someone over the phone to get into their freshly imaged computer. It does work.
This reset administrator password with no install disks is also known as using the command line or terminal. You first have to boot into single user mode, or hold the Apple and R key when the mac starts and then select the Terminal option under Utilities.
Of course if that seems too complicated and you have a usb drive or CD/DVD disk you can put that in your computer and hold down the C key to boot from it. Probably few people are using that option now since that was discontinued in the upgrade to 10.9 and 10.10.