Current flowing through copper wire?
As they will always tell you: don't short batteries out, they can explode.


First you look up the resistivity of the wire: Wikipedia lists 18 AWG wire as having approx 20 mOhm/metre
You have 0.25 metre, so you have 5 mOhm
IF the voltage stayed at 1.5 V you'd have V/R = I, 1.5/0.005 = 300 A
300 A is an awful lot -- it would melt 18 AWG cable in  a few seconds, for example
However there is no way to get 300 A out of a small battery
The typical short-circuit behaviour of a battery is still dangerous: a high current (12 A), a very rapid (3 seconds) rise in temperature of the battery -- over boiling, perhaps 120 C and a very rapid decrease in current as the energy is used, followed by a slower decrease in temperature. (Taken from battery manufacturer graph )


Measuring that would be tricky and require good safety work.

I'd suggest it's not a suitable experiment for grade 12 without considerable supervision on safety, and indeed how to capture the measurement quickly.