It can be VERY tempting to correct a child's spelling, letters, numbers, and mathematics. Many of us who did not get to experience a Montessori education were even taught using this style from our own early years teachers. However, the Montessori Method really strives to allow children to correct their own mistakes, when they are ready.
In the above photo, two of our students and practicing their Phonetic Spelling using some Common-Word Objects and the Movable Alphabet.
You will notice errors in their spelling choices; KEY is spelt "keu", CORN is spelt "kon", and FROG is slept "frag". This is completely ok!!! And there is NO need for adult correction!!
When your child is practicing their Phonetic Spelling Skills (which is sounding out words to figure out which letters are within), it is VERY important to remember the Aim of this work; it is not about correct spelling - it is about learning to distinguish phonetic sounds and letters within words!
So, as hard as it may feel in the moment, please hold back on correcting any spelling mistakes your child WILL make (and yes, I do mean WILL, and not MAY!) and let them know you are seeing the true accomplishments they are achieving - their phonetic spelling skills refinement!!
The Montessori Child will eventually see any spelling mistakes for themselves as a self-learner, and make the necessary adjustments moving forward. This could be at age 4, age 5, age 6 - and keeps going higher as the complexity of the words increase.
This is the same principal for inverted letters and numbers (which is a very common preschool stage - printing some, but not all, letters or numbers backwards). And the same goes for Mathematics, like Addition, Subraction, Multiplication and Division. Children will self-correct their mistakes when they are READY - this means when the connection forms cognitively, they see the error, and understand why it is incorrect.
So give them time, and fight back that urge to say "are you SURE ten plus eight is eighteen? Maybe count again..." Or "hmm... Is the bumps on the inside of the "B", or the outside...". As harmless as this may seem, it is derailing all of the hard work and foundations your child has built as a self-learner; because they will start to become dependant on an outside source (like a parent, teacher, etc) to check the accuracy of their work. Instead, be patient - and trust that your child will see the problem, when they are able!
Because they have formed a solid foundation of self-motivated, self-correcting learning styles, this will evolve on its own organically!