I have nicknamed this room the "Trash Room" because literally EVERY single drawer, cabinet, container, surface had tons of TRASH in it. I am talking like in the movies where they open the closet door and stuff comes falling down full lol. So when you see the before/after pics: it wasn't that cut and dry.
I worked with a lot of kids where the parent wants the room cleaned but wants the child to help so today I worked with a 16 year old. I have a lot of experience working with children from 10 years as a Store Manager training 16 years old for their first job to being a basketball coach to my son's basketball teams. Anyways we worked as a team. Once I realized how much trash was there, I would pick an area and have her throw all the trash away while I started dumping each bin to sort.
Because EVERY drawer was a junk drawer with no system, we had to wait till we went through the entire bedroom so I could see what actually would be left. Then after her trash duty was done- I would have her go through the piles to see if anything could go. After that, we started getting everything put away. If you see the wooden bookshelf area with the HUGE collection of hand sanitizer- that was completely done by her. She is the one living there and wanted to have it her way, which is okay if she will keep it neat.
With any kid's room the biggest thing is the parent really keeping a check on the room. Depending on the child, it might be looking in every day, every week, or once a month. I was organizing later in the day business paperwork in the house and the mother went to see the room....... and she had already put stuff on the floor. Soooooo we are going to say this room will have to be a once every day check until it starts always being cleaned up. If not, it will become a disaster zone fast.
What I started also telling people to do and I also will do for them is to take pictures of everything organized. Then if it gets messy, they have reference pics to quickly tidy back up. Then there is no thought to it, you just copy what was set up..... well unless you have gotten more of an item or gotten rid of a ton: then you have to reevaluate your system and come up with a new one.
All and all: a system won't work unless you do the work.