The sum checksum can be forced to any value, and here's how
Colliding the Sum Checksum (2019)
The sum command-line tool uses a 16-bit checksum that is trivially insecure. I wrote a tool that, using a meet-in-the-middle attack, can set the sum of a file to any desired value by inserting bytes at a chosen offset. The attack exploits the reversibility of the sum algorithm and the small hash space, finding collisions in a split second. This could let a student forge a file that matches a previously submitted checksum.
Using a non-cryptographically secure hash for this task is totally insecure, as a malicious student could find another file which has the same checksum as what was submitted on the paper handout.