I keep all the mothers/father's day things they make and toss the rest - I used to keep it all when DS1 started school but we just don't have the room to keep enough work for 4 kids! Plus our school does a 'worksample' portfolio every year where they get the kids to do 'worksamples' of the different things they do over the course of the year which covers all the KLA's so at the end of the year they bring home a nice and tidy A4 display folder full of all their best work which I get to keep and that works much better. So now I just toss everything as it comes home - paintings I usually put on the fridge for a bit and then toss when the next one comes home.