A negative to dressing professionally is a teacher should be aware of the level of comfort involved with the clothing. In an elementary level, a teacher needs to be able to move freely, as different activities could involve a variety of twisting and body movements, which could expose body parts, or if shoes are not appropriate for movement, can hinder on an activity. It is possible to be professional and comfortable.
References
Wong, H., & Wong, R. (2009). The first days of school: How to be an effective teacher (4th ed.). Mountain View, CA: Harry K. Wong Publications.