On an unweighted GPA scale, a 4.0 is the highest a student can achieve. A cumulative 4.0 GPA means that the student made straight A's throughout the entire time frame included in the calculation.
Some high schools use a weighted system for more advanced classes, such as AP or honors courses. An unweighted scale uses 0.0 for an F, 1.0 for D, 2.0 for C, 3.0 for B and 4.0 for A grades. Not all schools use the same weighted system, but generally, a weighted A is worth five points. Different levels, such as pluses and minuses attached to the letter grade, give partial points in many systems. For example, a B- may be worth a 2.7 in some schools.