It took me ages to train dh and the dses to recycle, and none of them have really grasped it yet. Dh still puts envelopes in the recycling, and plastic bags/food wrap.
He had just about learned what could and couldn't go in the recycling, when we moved, to an area with very different recycling rules. I spent the next 18 months teaching him the new recycling guidelines - like not recycling meat trays (washed), or carrier bags, both of which our previous council accepted for recycling.
Then the bastards council changed the guidelines again, and we are back to square one. Now we can recycle meat trays (washed) and tetra paks, and we don't have to separate things the way we used to - but dh still hasn't gotten to grips with this.
I used to have a notice on the recycling bin, listing what could go in it, and I would still find the wrong stuff in there.
The dses aren't much better either - I do have to fish stuff out of the ordinary bin to put in the recycling, and vice versa.
Perhaps it's something to do with testosterone?