Skill
Skill Grades
Each trained stat has a level and a grade; higher grades make the same level contribute more skill points.
Level and grade
Grades range from E through S. At level 50, an E-grade stat contributes 500 skill points and an S-grade stat contributes 1,000. Raising a grade does not mean the duck has gained the same number of training levels.
Education
The 
School improves grades over time. Use trained residents and appropriate 
Equipment to prepare for different course demands.