The research shows that at best, worksheets can be used to teach skills that children could learn without worksheets. Any foundational skill that could be taught through a worksheet can also be taught with a hands-on activity. For example, to teach children how to recognize and write their name, teachers could hand out name-tracing worksheets every day. Or, teachers can label things with children's names and talk with children about the letters they see, play games where children match stickers, magnet letters, and other letters to their names, and provide name cards so children can write their own name on their artwork. Which of these methods do you think a preschooler would enjoy? We know which one we'd rather do!
At worst, worksheets can teach preschool children that they are bad at school, by requiring them to complete tasks that they aren't physically, mentally, or emotionally ready for. Most three-year-olds, many four-year-olds, and even some five-year-olds simply don't have the attention span to sit down and do paper and pencil tasks. It's not interesting to them, so they aren't intrinsically motivated to do it! Additionally, many children in preschool won't have the fine-motor control to successfully complete even worksheets aimed at preschoolers. A worksheet that requires children to use a pencil with precision is setting most preschoolers up for failure-- they need lots of time to practice using writing materials in their own way before they'll be able to be successful with worksheets! All worksheets by nature require a great deal of fine motor control and experience with using writing materials, and children who always struggle with worksheets because they don't have that fine motor control can become resentful, or even anxious about school.
Even if the worksheets don't cause a child to experience a lot of failure or boredom, they aren't usually an effective way to truly teach a concept to preschoolers. The article from Early Childhood News gives many examples of this, but to make a long story short, sometimes when a child can successfully complete a worksheet, all it means is that they know how to complete a worksheet. If children can successfully chant the letters of their name and write it on worksheets, does it really mean anything if they can't recognize their name on their cubbies or write it on their artwork?
That being said, some children really do just love worksheets. We're not saying that we would ever tell children "No, you can't do that worksheet, it's not developmentally appropriate!" In fact, Lisa's son, my brother Jacob, loved to do worksheets as a preschooler and requested new workbooks almost as often as toys. What we do believe, and what the research supports, is that the bedrock of a preschool education should be hands-on, authentic learning experiences that follow the child's interests, rather than sit-down, pencil and paper activities that follow a teacher's plan.