SBG in a non-SBG world

My school uses PowerSchool and a grading scale which is required by the school board.  I have spoken to both the vice principal and department chair and they are interested in Standards Based Grading, but they also seem hesitant to allow a single member of a department to deviate significantly from what other members of the department teaching the same class are doing with regard to grading. I've been told that I can make changes within the approved structure, but I cannot just throw it away.

Currently grades in the math department are calculated by using the following system:
20% final exam
40% Tests (and these are common assessments, given by all members of the department teaching a particular class)
20% quizzes (there is some wiggle-room here as these assessments are not necessarily common assessments)
10% homework
10% teacher's discretion  (traditionally I've used this as a participation grade based upon warm-up compliance and general participation.)

The first 3 listed above are pretty much written in stone.  These are the ones I really cannot change.  With regard to the 40% test category, we already do give students the opportunity to reassess the complete test (which covers either half or full units).

The common assessment tests are how I will either show that my attempt to implement Standards Based Grading is having an effect or is not.  I like the fact that these assessments will require retention from my students, which I see is a possible pitfall of most SBG systems I've encountered.  I will need to take the "common assessments" we have created and cluster the questions in such a way that I can more easily evaluate student comprehension across the standards, but otherwise these tests will likely be the same as those given in other Algebra 2 classes in my school.  Reassessment will be Standards based rather than whole assessment based as the department currently does things.

I will be modifying quizzes to be standard (or skills) based so that I can more easily determine where a student would need to reassess.  This would allow me to reassess particular skills rather than reassess a complete quiz. Also, my students will be assessed more frequently than other students in Algebra 2.  Students who will need to reassess will not receive a percentage grade, instead they will get strategies for reassessment.  The 10% teacher discretion points will factor in here. 

I want to add an additional kind of quiz as well.  I want to implement what I am calling "Mastery Quizzes". These quizzes will be focused on skills from Algebra 1 (or previous semesters in Algebra 2) in which students should be computationally proficient.  For the first trimester the "mastery quizzes" will focus on solving equations (probably 2 of them) and working with exponents(most likely 1).  These quizzes will contain 10 questions, and students will have to perform at the 90-100% level in order to not have to reassess. In later trimesters these quizzes will include factoring, completing the square and other topics I have noticed that students struggle with when we reach later units (ie, rational expressions and conic sections).  My teacher discretion 10% will factor in here as well. 

Homework:  Here's my thoughts on homework.  I have basically been told homework needs to a component of my grade scale.  So, I am leaving it as 10% (department policy) but I am grading each homework assignment as 1 point (which means first trimester should include approximately 35 - 40 points here). Another component of this 10% will be the Interactive Student Notebook.  The ISN will be worth 100 points.  Lastly, any student getting Mastery level on any standard (skill) will receive full credit (whether completed or not) on the homework related to that standard (skill).  So, potentially it is possible for a student to receive full homework credit and not have completed a single homework assignment.  

What does this look like?  Good question.  Here's a snapshot of my changes:

20% Final Exam
40% Tests (with reassessment on any major standard which is below proficient)
10% Homework (ISN and homework as described above)
30% for quizzes:  Mastery Quizzes will only count toward the 10%.  Standard (skills) assessments will count towards the 20% (department mandated) and the 10% as well.

My original thought were to make the quizzes worth a total of 40% and tests 30%, but it was pointed out to me that if what I am doing works then the 10% shift really wouldn't greatly affect the grades.  Making such a shift, would potentially make comparing my scores with the scores of other classes teaching Algebra 2 difficult and such a shift would also require school board approval which might be difficult given that no one else has tried using such a grading system previously in my district.