Is it possible that when a student hasn’t finished an exercise at the end of the year he continues in the next year? So you don’t work with school years and evaluate cross-school year?
Is it possible that both a teacher and a mentor at work can evaluate the student, within the same course?
Can a teacher evaluate his students without participation of the student, without the need to submit any assignments?
Can a teacher see the evaluations of the students of his groups at least twice a day and can they adjust it?
Can a teacher or mentor at work see the whole evaluation of his students, including the evalutations registered by other teachers or mentors at work?
If your school has a non-standard structure, you could choose to use a single school year that spans multiple years. Some people have used this as a way for data to persist from year to use. There are knock-on effect, such as having to handle school year rollover manually.
Gibbon has many different ways to assess students, such as the markbook, internal assessment, and formal assessment modules. It also has external modules, such as Free Learning, which offer even more flexible ways to build courses. It may help to check out the documentation and extend page to see some of the capabilities.