I was recently asked this question by a reader and thought I'd share what I do and quiz you guys about how you do it.
For the last 3 years I've kept each child's work in a file folder (prior to that we tried notebooks but they were never big enough).
Each girl is given a folder with a few tabs in which are then labelled by subject.
At the end of each day any notes taken, posters drawn, notebook pages, stories/poems written, experiments recorded, artwork, worksheets etc are placed in a file tray. At the end of the week (or sometimes every couple of weeks if we are feeling lazy) they get the hole punch out and file them away.
For any of the bigger stuff (model of the pyramids, large art pieces, historical feasts, educational games, lapbooks, trips) I just take photos that I can print and place in their folders.
I also do this for any Montessori materials they use - for example, when they were doing the adverb presentation I took photos and popped them in her folder.
With their 'internet learning' there are often print outs of the lessons available, otherwise I print out a report from the parents page to include.
With 'video learning/youtube learning' they take notes while watching which get included in their files.
So how do you record your child's work?