We used to critique our Montessori equipment with our directress who was a developmental child psychologist. She suggested once that the solid geometric shapes were wonderful for tactile experiences and vocabulary for geometry. Her improvement for the shapes would be that they were clear and you could measure the volume of each shape.
This is something she would have liked! The lids can be removed. Measure volume using millet in a measuring cup and grade the shapes from the largest volume to the smallest volume. It's a great Montessori lesson.
Montessori introduced the sounds of letters first, then spelling 3-lettered phonetic words and lastly, reading phonetic words. Check out the word list at montessorimom.com for words to spell and read for your early reader.
Montessori used the moveable alphabet to teach spelling. My children loved this activity.
Reading readiness for preschool children is as easy and fun as using two-part cards. Children match objects to a picture. This helps a child take a 3 dimensional object and match it a two dimensional card. This process helps with the transition to reading.