Add some explanatory text:
Categories are used in SchoolTool's gradebook to organize activities and to allow teachers to weight different types of activities differently to calculate grades. For example, the grade in a section might be comprised of 60% test scores, 20% homework and 20% class participation.
Currently, the list of available categories for all teachers is managed through this form. That is, if one or more teachers would like to use a category not in the current list, the site manager can add it here. Likewise, if some of the default categories are not relevant to your school, remove them below.