In years past, people dressed in their "Sunday best" to attend church. There is a healthy principle behind this tradition, desiring to honor God by "dressing up" to worship Him. In recent years, many churches have emphasized casual attire in order not to make the unchurched person who attends feel uncomfortable, having no understanding of the church's traditional expectations. This has happened in a broader culture shift towards dressing casually.
Whether your church observes the tradition of dressing up or worships casually, you should be aware of the potential barrier to visitors. Arriving dressed up more formally than the regulars can be just as embarrassing as dressing too casually.
Truly, your church should welcome the visitor in, overlooking how they look, focusing on the person in need. This may be accomplished by avoiding any comments about dress, and by personally befriending the visitor for the duration of both the Sunday class and worship hour.