Do MECS programs keep track of errors??

Yes.  After a lesson (where appropriate) errors are noted on the screen.  Instead of advancing to the next lesson, the Continue button will return the student to the beginning of the same lesson and they will be invited to repeat it.

MECS software encourages a sense of mastery to build on further complex levels of learning.

However, you are still not "locked in" since you can return to the Menu to make another choice of lessons.  You are "in command" at all times.