Here's an outstanding resource for all orchestra directors, from the newest to the wisest veterans. Orchestral Bowing: Style and Function includes a textbook with extensive details on the bowings - how they are played and how they are taught; and a workbook for the players to use an ensemble. The workbook is in a score form so that Violin 1, Violin 2, Viola, and Cello/Bass all have the same book on their stands, and all learn the bowings together. These two books could greatly improve the skills of your players!