At the end of every school year, I spend about 2 hours filing, sorting, and organizing our school workbooks, art work, pictures, and any other school-related keepsakes from the entire school year. I've been using this system for a few years and we absolutely love it, so I figured if it works for us, it may work for another family as well!
We use two different items to organize our school memories: a hanging file folder bin for each child and a First and Last Days of School Keepsake Book (they also make a more boy-ish version here).
For the file bins, we had someone locally create these for us a few years ago, but basically you can write the child's name on the front, use a Cricut to cut their name on sticker paper to put on the front, or adhere a label to add the child's name. Each girl has a color assigned to them and all the hanging file folders are that color and there is a label on each folder with the age (age 0, age 1, age 2, preschool year 1, preschool year 2, kindergarten, first grade, etc.), but you can make this as simple as you want to!
I start by collecting all workbooks, notebooks, student books, art work, crafts, etc. from the year. We keep all our school books we use throughout the year on a rolling cart in our dining room, so that's really easy to find everything. As for the artwork, I save artwork my kids may want to reference/work on again or that is realy special (as well as keepsake items they receive throughout the year - thank you cards from people, sports records, etc.) in a wooden bin in our kitchen. Usually about once in the middle of the school year, it reaches the shelf above it so I go through it and recycle a bunch of stuff. Then, by the end of the school year it's normally piled up again so I then go through it all. I am pretty ruthless with this. If it's not something super special (like a sweet card they made for their sister, a certificate they got for doing something, etc.) or representative of their current skills (like a coloring page they just scribbled on or something), I receycle it. I only save things that are super special, meaningful, or are a good represenatation of their current abilities when it comes to drawing, painting, etc.
Then, I go through all their school notebooks, work books, etc. and rip out pages that are representative of their best work or show something they worked hard to learn. For example, in a math workbook, I will rip out a lesson usually from each unit in the workbook that is a good example of their learning at that time and then I will rip out the final assessment to show that they understood the entire course. For their notebooks, if they are very full, I will often rip out extra pages so it's thinner and any "fluff" page or pages that weren't worked on as hard. I am aiming for their best work and a good representation of what they learned that year. Then, I take it all and add it to that year's file folder in the file bin.
After the file bin is filled for each child, I move on to the keepsake books. I make a list of the photos I need for each child. There is a spot in the beginning of the book for a school photo from that year, and since we homeschool and don't typically take school photos, I print a 2"x3" photo of their first day of school photo. Every year has a spot for a 4"x6" first day of school and last day of school photo, so I include those. I go into my phone where I keep a folder of homeschool photos from the year in an album and I go through and select the first day of school and last day of school photos and then various photos for each child of things we did during the year. I bring these into Canva and resize them for each spot. The random photos from the year I just make various different sizes to add to the photo spreads in the book.
I print the photos out on to glossy paper just using our inkjet printer (we have an older HP Envy photo printer that we use for all printing in our home), cut them out, and then I use a tape runner to adhere them to the pages. The book includes many spots to write in information about your child, so I fill that out as well.
And voila, I'm done for the year! This takes me about 2 hours at the end of the school year and that's it! The beauty of this is how simple it is but also that my children will have not only a beautiful keepsake book and a bin (maybe two) of school work from their childhood! My parents kept a ton from my childhood but it was all put into large bins (which I am very grateful to have) and so I have never taken the time to go through it all because it's daunting to do now as a 35 year old! I didn't want to hang on to that much stuff for each of my kids and I also didn't want them feeling resentful of having to decide what to keep as an adult, so I'm really happy I started this system right away.
However, even if your children are in high school, you can still do this! If you want to go back and do previous years you can, but if that's too overwhelming, just start where they are right now! It's better to have something than nothing at all!