This is a versatile and engaging strategy – also great for a portfolio: write it now and evaluate it at the end of the school year.
It can be done several ways.
One method is to just begin writing – maybe time it – and get everything down you want to write. Here is a sample: https://www.powerpoetry.org/poems/random-autobiography 
Another version is to give each student an envelope full of paper strips (at least 15), and over the course of a few days or weeks, invite students to respond to a question or reflective statement, express a feeling, or write an “I learned…” statement. Then at the end of the days or weeks, invite each student to empty the now full envelope and arrange the strips to their liking and either tape or re-copy onto a new piece of paper. Voila! Random autobiography about school.