Size is likely 0 because it’s locked and it’s also not likely formatted for NFC. All NFC tags are also RFID tags, so obviously they can be used for non-NFC applications… but the NFC forum requires that tags like the Ultralight, which is an NFC Type 2 tag, must have a “capability container” that is formatted for NFC… the capability container tells the reader that this tag is meant to be used for NFC applications and relays the size of user memory bytes that can be used for NFC applications. It is not likely that this student card is formatted for NFC, so the size is 0.
Also it’s hard to know if the card’s serial number is used exclusively or if it also uses the user memory contents… but in just about every application I’ve ever seen, the serial number is always used in some way. As @Jaroot said, we do not currently have an implant which can support cloning an Ultralight serial number and contents.