The typical grades awarded for participation in a course are (from highest to lowest) A, B, C, D, and F. Variations on the traditional five grade system allow for awarding A+, A, & A- ; B+, B, & B- ; C+, C, & C- ; D+, D, & D- ; and F. In primary and secondary schools, a D is usually the lowest passing grade, however there are some schools that consider a C the lowest passing grade, so the general standard is that anything below a 60 or 70 is failing, depending on the grading scale. In college and universities, a D is considered to be an unsatisfactory passing grade. Students will usually still earn credit for the class if they get a D, but sometimes a C or better is required to count some major classes toward a degree, and sometimes a C or better is required to satisfy a prerequisite requirement for a class.
Below is the grading system found to be most commonly used in United States public high schools. This is the most used grading system, however, there are some schools that use an edited version of the college system.
Below is another grading system used by a few different colleges in the United States. Other schools use different systems, so this is by no means universal.