Bad boundary behavior in star invariant subspaces I

We discuss the boundary behavior of functions in backward shift invariant subspaces $(B{H}^2{)}^{\perp }$, where $B$ is a Blaschke product. Extending some results of Ahern and Clark, we are particularly interested in the growth rates of functions at points of the spectrum of $B$ where $B$ does not admit a derivative in the sense of Carath'eodory.