Most Montessori activities have a control of error built in to the work. For example, on a cylinder block each piece fits correctly in only one particular hole.  In a classification exercise, each category has the same number of objects.  A pitcher to be filled by a child has a piece of colored tape inside to show the child to what level the pitcher should be filled to have the best chance of successfully walking from the sink to the work area without spilling the contents. 

Some activities do require the control of error to rest with the adults or older children.  One example would be in the Math area.  Let us say that the child is multiplying 5 times 4.  That is 5 taken four times, so the child would remove four 5- bars from the multiplication box
(A box with wire bars of beads insets from 1 to 10).  The child then counts and may get a different answer.  The adult would then say “Let’s count this again,” and may touch each bead as the child counts to help establish the one to one correspondence of object to numerals.  Or the teacher may say, “You need to count this again.” In both cases, the child has been told that he/she does not have the correct answer, but is also told by the manner of correction that he/she can get the correct answer, perhaps with a little help.  This is very different in the building of self esteem than saying, “You are wrong”