Understanding the Grading System

Spent the day with Excel and working with teacher grades. First day I haven't been in the classroom. The classroom is much easier.
Student grading is based on a 20 system here. All scores on all assignments and test are converted to this system. Mathematically, this is not a problem for the most part. However, converting to the 20 system BEFORE calculating grades causes all kinds of injustice. If you violate some basic rules of math, you should expect this. Teachers were totally unaware as to what was happening.
For example if you have three assignment of differing lengths and values and convert them to the 20 system and then average them, really bad things happen. Assignments of 30 points, 50 points, and 5 points could result in students getting less total correct answers getting higher scores on the 20 system then a student with more total correct answers.
Friday, school is over at 10:00 and we are going in to a major "how to grade" workshop. Because I don't have the Spanish, I need to generate several examples of what NOT to do and have my co-teacher understand it thoroughly so he can explain it in detail to the entire staff. I just can't stand seeing students get the short end of the grading stick because adults don't understand the math behind their grading.
More later!!!!!!!!!!