I've been asked this question a lot and since I've worked in both environments, I feel at least semi-qualified to answer. My answer is solely based on the experiences I have had, so others may disagree with my response, but here are my thoughts.
In a day care setting, the children have to be there. Their parents are working & they need a safe place with caring adults to leave their children during those hours when they have to be away. Day cares typically provide custodial care, that is, being a stand-in for mom & dad during the hours when they are away. That includes caring for boo-boo's, loving & snuggling the children, teaching & guiding them in not only academic ways, but also with morals & values & basic standards of life. They are also responsible for disciplining them when necessary, feeding them, putting them down for naps and help with potty training from day 1 to completion while the children are in their care. Day cares will vary, but in the one where I worked, it was mostly staffed by college-aged ladies who were there for a semester or two & then left. While this is certainly alright & the children got quality care from these ladies, there were times when I felt bad for the kids in their care who had gotten attached to them & then had to watch them leave. There were a few older teachers who had chosen this as their career, who were involved in the center and its children for many, many years, so there is a wide array of teachers & experience in day care settings. Day care centers provide oppurtunities for the children to learn with curriculum-based centers and group times, field trips & outdoor activities, but they also provide a lot of 'babysitting' & free play time because you really can't have every minute of the day lesson-planned out. Day care centers are generally open from 6:30 or 6:45am until 5:30 or 6:00pm and offer care for infants all the way up to 12 year olds in after-school programs. Some day care centers offer meal programs for the children as well.
In a preschool setting, the children don't have to be there. It is a choice their family has made to provide a pre-elementary school experience for the child. Preschools are typically open fewer hours (many are 1/2 day programs) with a much smaller age range of children (usually 2 -5 year olds). Preschool classes are specifically designed to introduce children to a classroom setting & prepare them for the routines & structure of elementary school. Curriculum is fun & exciting and provides lots of oppurtunities for hands-on activities and crafts. They also have field trips and outdoor activities, like a day care center. Preschools do not usually have nap times because the children are only there for 3-4 hours at a time. The kids may have a snack and/or lunch at preschool. In a preschool setting, teachers are typically ones who have chosen to teach in this sort of setting as a career, not just a job (there is a difference!). Parents of preschool students may be working, but many are not. They have simply chosen to implement a preschool program to prep their child for Kindergarten. Preschool teachers will, like day care center teachers, provide love & care and nurturing, first aid for boo-boos and discipline when needed.
Of course, there are a lot of day care centers that are now moving in the direction of preschools & even may carry the "preschool" title. There are also preschools who provide an extended time frame for families with working parents. So while there are situations where the 2 names can be used interchangeably, there are most definately some very big differences.
One thing both environments have in common is state licensing & guidelines they must follow regarding care, health standards & teacher requirements. Teachers in both situations must go through ongoing training classes to stay "on the top of their game". Schools vary with regard to teacher licensing & credentials. At both of the places I have worked, teachers must have (at least) a high school diploma, first aid/CPR training and experience working with children, with preferance given to those with a degree or some college classes in early childhood development. In both environments I have seen teachers on both ends of the extreme---some with teaching degrees and some with only a HS diploma.
After having worked in both environments, I can say that I really prefer to be in a preschool. While my time with the day care center was absolutely fantastic and I wouldn't change it for the world, I adore the preschool environment for a million reasons. If the time came that I needed to transition back into a day care center, I would do it but I prefer a preschool.
Any questions? Feel free to leave a comment or email me: Lizreeves2@aol.com