Standards Based Grading

For about two years now, I have been mulling over the idea of SBG for my special education resource level Algebra 2 classes. I have just really been struggling with implementation. We have classes of varying length (some periods are 48, others are 54) and I often feel like this is not long enough. At the same time, if I did have single skill based quizzes, the assessments would not take as long.

My main issue is when to offer re-takes. I do not have my own classroom. This really puts a damper on having students come in early or stay after school for extra help or to retake assessments.

I am currently deciding if it would be feasible to have a "quiz re-take day" once every two weeks or so, where for 15 minutes during the period, students could re-take a quiz. My issue with that becomes what if they need to retake more than one?

Also, what remediation must they complete in order to be eligible for a re-take? My students do not complete homework, so most of them would never be eligible for a re-take if I required an assignment to be completed.

Hmmm... lots of thinking to do before next school year. I would not want to begin a new grading system partway through the school year anyway.

Any suggestions for a newbie like me?