We rotate our toys and materials for two reasons:

1. We only want a few materials out at a time, so the child isn't overwhelmed, so they can look after their materials and maintain order. In any one area I've found 9-12 materials about right for an infant/toddler.
2. We want to keep the child interested in their toys and materials. Often if the child isn't using a toy we can put it away for a couple of weeks and then get it out again and the child may have a renewed interest in it. It also prolongs the life of our toys and materials. 

For many families, there is a third reason and that is often they have too many toys to use at one time. Sometimes it's Christmas or birthday time, when the child is totally swamped with presents, rotating what is on the child's shelves means they all (or most) will get used and played with! 

I have a few 'rules' or guidelines on rotating toys, I don't stick to these 100%, but this is what I aim for:

• Observe your child, while playing, while working. Make a mental note of what materials they are using, what they have mastered and what materials they are not using. 
• Consider the materials the child is not using, are they age and developmentally appropriate? If not put them away. If they are, does the child need a lesson on how to use the material or could you use it together to spark an interest? If the child is lacking the skill to use the material is there another way of teaching or introducing that skill?
• Consider the materials the child is using, what is the next step, what is the next skill they will master, are there toys that we can order now to have when the child has mastered these? I am always thinking one step ahead of my child, so I have puzzles and a few toys put away ready to use in the next couple of months. 
• Assess and rotate materials on the shelves every week. Often this is a quick tidy up or refresh and I might only rotate in or out one or two toys. At other times I might change 5-6 toys. I never rotate all of the toys at once. I don't always do it on the same day but I try to do this weekly. If I find Otto has stopped playing independently, is unsettled or lacking concentration, sometimes I will find that it's been too long since I have rotated his toys.  
• Always keep out most used and favorite work. We've had some work stay on the shelf for 12 months or more. If the child is really into a toy, leave it on the shelf, only take it out of rotation when or if the child has lost interest. Keep out favourite materials even if you think they are 'too easy' for the child, your child may be enjoying the repetition in using the toy and they could still be building skills, coordination and concentration. 
• Also rotate books, items in discovery baskets, nature trays, sometimes musical instruments in the music basket. I use the same principles, I rotate out what isn't being used and keep the favourites. With books, this often means rarely changing them or only rotating one or two books at a time. 
• Rotate big toys, I apply the same principles to larger toys like our wheely bug and trike. Our Pikler arch, wooden barn and, ball tracker have always stayed out but I would consider rotating them if they weren't being used.
• Consider changing the location of toys if they aren't being used. I often move toys from Otto's play area (downstairs) to his bedroom (upstairs). While there are some materials I wouldn't put in his room, often moving them renews an interest. 
• Try to keep the materials not being rotated in the same position, young children thrive on order and may find it distressing if their favourite toy has moved.
• Rotate toys while the child is present. This is personal and I haven't read much Montessori opinion on this. Other than we want the child to own their space, I don't want him to wake up one morning and find his whole play area changed. While Otto is sleeping I might get a few things out of the storage box but I do the actual rotation with him present.
• Remove any toys with missing or broken parts. This is more important than it sounds but we don't want our child to use the materials in a state of disrepair and if it is missing a part it may be missing the control of error.  
• Clean the toys and materials weekly. While I am rotating toys I will often clean the toys staying on the shelves, usually this is a quick wipe over with a cloth. The shelves shown above and below are next to a window so may get dustier than your toys but they generally need cleaning (quick dust) every week. 
• Consider rotating plants and artwork. This is also personal. Order is important to the child and some plants just have a favourite spot, but I like to occasionally rotate the plants and artwork in our children's spaces. Artwork, I would rotate no more often than monthly but at the moment it's really at the change of seasons. 

The wonderful thing about rotating toys is often the child will become deeply interested, and engaged with some of their old toys. It's a rewarding process where the end result is more concentrated play! 

Recommended reading:

• Why Shelves Work Better Than A Toy Box 
• Beautifully Organised - Montessori Shelves 
• How many activities should I have out - Montessori Toddler