I'll bite oblomov seeing as you think you're a competent lead teacher.
Accuser wanders in at 1.15 saying he's been beaten up by OP son. He's had time to get a couple of his mates briefed on the story. You park him in you office to write his statement, and send staff to round up his mates and get their statement. You don't know where OPs son is so are going to have to wait till pm reg to collect him.
You request and review CCTV. Unfortunately its inconclusive - you can't tell as the person committing the assault has their back to camera and a hood up.
You now have 3 statements to review and questions to ask. OPs son is in a side room waiting to be interviewed. By the time youve taken statements and talked to all 4 so far its end of day 1.
Day 2 - you've identified people corroborating OPs sons story and some other witnesses from the accusers story. By now its clear there is more than one story here. You collect all these witnesses, take statements, review and question. By now its lunchtime and these statements have identified a wider pool of witnesses. You start to collect these and question. Day two ends.
Day three - you've reviewed all statements and have further questions for key witnesses. You spend most of your day chasing these down. By end of day you think you have a clear picture of what is going on and discuss with head.
So tell me again how you were going to collect 20+ witness statements, interview 20+ kids multiple times, and do your full time job in 30 minutes?