Schedule changes happen and when a student moves from one teacher to another, grades do not transfer. Grades must be manually moved or a transfer grade can be entered in the new teacher's gradebook.
There is not a simple way to add in the transfer grade. Below are a couple of options.
Works for weighted or non-weighted gradebook
Enter a grade for each assignment, that was given before the student entered the class, that equals the desired percentage for the max point value of the assignment. For example, if the B- equals 80%, if an assignment has a max point value of 50 points, enter a score of 40; if the assignment has a max value of 20 points, enter a score of 16, etc. It would take some calculator work to determine the score for each assignment. Enter these on the student scoresheet and in the comment box, enter Transfer Grade. You can copy/paste the text for each comment box.
Works for weighted gradebook only
For each category, calculate the total of the max points given for the category before the student entered the class. Example: If "Assignments" is one of the weighted categories and 300 points were assigned before the student entered the class, create a new assignment in the Assignment category with a max point value of 300. If B- equals 80%, enter a score of 240 for the student. Leave the other students blank. You can also enter in the comment section for the transfer student, "Transfer Grade". Repeat this for each weighted category. You can view the number of points you have in each category by clicking "All Grades" at the top of the gradebook page.
Works for non-weighted gradebook only
Create one new assignment worth the max points available for all assignments entered before the student entered. the class. Enter a score for the student that matches their incoming percentage. If the student is coming into the class with an 80%, for example, and the max points for all assignments to date is 1200 points, then enter a score of 960. 960/1200 = 80%. You can also enter in the comment section for the transfer student, "Transfer Grade". Repeat this for each weighted category. You can view the number of points you have by click "All Grades" at the top of the gradebook page and looking at the Points column.