18 months is WAY to young to be spearated from mama, especially if he doesn't absolutely have to be. Wait, wait , wait, as long as you can.
Weather or not a child has preschool makes no difference on weather your child will excel accademically in school. No child will learn a concept any earlier than what the brain is already prewired to do. Just as your child wouldn't be able to run at 6 months old.
Trying to push educational concepts before the brain is ready is one of the reasons kids get fustrated with themselves and put up future mental blocks. Just as we wouldnt expect a 6 month old to run because their brain/body is not ready, so it is with other learning too.
I venture to say that young children who are well bred, engaged and disciplined- by the parent in a home atmosphere, fare better overall and certainly on social skills than those who are put into the pack .