What does an "A" mean? Does an A mean that a child understands the material? We all know students who are very intelligent but so... lazy. Does their "D" in a class mean they don't know the material? What about students who struggle and only get 1 question correct on a 10 question quiz? The next week they get 3 questions correct. They have just increased their score from 10% to 30%- should this not be celebrated?!!
Grading is so tricky as people are fearful to stray from letter grades but here is an idea if you're open to a change. It's adapted from ideas included in this chapter of Fair Isn't Always Equal by Rick Wormeli. It's such an amazing book and one you'll want to add to your collection!
Make a list of all objectives you'll cover in a unit and list them all as you would assignments in your grade book in a separate space. Continue to maintain a regular grade book in case parents would like to see your data. Once you feel you have enough data to determine that a particular child has mastered an objective, check off that they have completed that objective in the grade book. At the end of the unit, count up total objectives mastered and divide by the total objectives for the unit. The result is their grade for the unit. All the regular grades you took were simply data to inform your decision- not to determine it.