The gradebook was designed around the principle of continuous evaluation. As the school year proceeds, more assessment items are added, and the students' averages will/may change. The gradebook does not have a concept of term 1 average, term 2 average although it can be adapted to that approach. When posting to the report card system we are only taking a snapshot of the student's continuing progress.
Each item has a group membership and a weight. You could create a series of term 1 groups, term 2 groups, etc. You can then adjust the group weights throughout the year to reflect the contribution of any group to the overall average. You would normally do this just before report cards and post this updated average into the report card system.
Students should have some feeling of ownership over their evaluation. The online gradebook results are (or may be) visible to students and parents on the OA parent portal site. This gives transparency to evaluation of students, which I feel is a good thing. It helps keep parents informed and onside with the teacher(s). Evaluation is what we, as teachers, do.