The part that always fell apart by October
I'd start every year with a fresh spreadsheet and the best intentions. By October the attendance tab was three weeks behind and I couldn't remember which readers we'd actually finished.
Now it's one quick log — a grade, a day of school, a book, a photo of today's math — usually from my phone before I forget. Tag it to whatever you're teaching from (TGTB, Masterbooks, Abeka, BJU, My Father's World, Apologia, Saxon, or your own), and it's waiting for you when you need it.