I never skipped school. My first sophomore year I just did zero assigned homework. None.  Even doing absolutely nothing I managed to pass one of my classes.  How that happened I have no idea.  That was Phsyics.  I crushed all of the exams with top marks but did zero other work.  I think the instructer liked me.

The next 3yrs were a very different story. A year at a beautiful amazing liberal arts boarding school run by a group of counter culture artsy hippy generation administrators and academics. It really was an amazing place.  Then, my repeat sophomore year, Jr, and Sr years at a military school.  Instant honor student, etc...  Standards.  Without any way to avoid accountability for deviating from those standards can work magic.  The model tends to force performance. Behavioral performance. Academic performance. Etc...

24/7 under the direct supervision of Cadet leaders, teachers, or administrators.   Once performance was proven, things were far less burdensome.  Everyone went through the initial 6wks of pure hell. Learning the structure, uniform set up, shoe shining, polishing floors with paste wax, the daily schedules, how to march, initial military science and leadership development courses, rank, hierarchy military courtesy, etc....   I am a path of least resistance guy so mastering it all was the obvious choice.  If you can't beat them otherwise, beat them at their own game.

So that is what I did.

I was raised by parents who had structure for our family.  The year without structure was like a kid in a candy store for me.  I had a blast. Military School was just an extension of my natural family environment and from day one I understood the basics.  Be alert, pay attention, innovate on the drudgery to do it better and faster than the tried and true, deliver on grades, be a leader since it was far more enjoyable than fighting the process.  Engage with teachers by being interested in the course content. Do the homework and do it well. Etc.

It was a challenge but for those who engaged it was could be a a great experience.  

Our kid was a midline academic performer on average. He figured out the system and owned the school the teachers, etc from there doing exactly what he wanted to do. He was polite, well behaved, and he really was the smartest kid in the class.  He hated attention so his comfort zone was to be unnoticed in the middle of class rankings, band etc...  Because he was truly that smart, he got attention and teachers would engage him to perform to his capabilities. The band director assigned him as the soloist for his instrument, teachers had him present his work, papers, etc... in front of the class.The work he did do he won awards for.  So first 6wks, straight A's. Second 6wks straight F's.  He knew that he could not be failed or held back unless he failed the same two classes two 6wks periods in a row.  Block scheduling started in Middle School so they had entirely different classes each semester. His first 6wks of stellar performance guaranteed him a pass for the semester.  It also got his teachers fully engaged in his fan club.  So the second 6wks he would read novels in class, etc. 

So, off to Military School. My family's school had closed 6yrs earlier than SS's Military School tenure or he would have gone there.  The school we selected for SS was incredible.  By the time of my tenure our family stradion school was in decline.  The campus was aging, the school was struggling financially, and the physical plant was tired with no money to maintain it. 

SS's experience was the same as my dad's, mine, and my younger brother's.  We all ended up at Military School under similar circumstances.  Smart kids, too smart for our own good.  Started at one school for a year (or two), then repeated a year and finished the rest of HS at the Military School. Like father.... like son(s) apparently.

SS was a rock star at Military School for his first year.  Then.... we made the mistake of getting him a laptop at the behest of his instructors.  Bad move.  He and the Spermidiot burned down that incredible opportunity with all night every night WoW bonding time after hacking the school firewall.

Anyway. like my parents did not tolerate or allow me to fail, we did the same for SS. His mom and I jerked a knot in his tail so tight that he cold not fart a mustard seed, scared the shit out of him, and rode him like a broke backed mine donkey until graduation.  We were on him like stink on shit.  No gaming. Nothing but school work and shoveling countless tons of snow all night during a series of record snow storms.  His graduation was a sullen event as he was not at Military School. He loved that school but screwed it up so we were not paying another 3 semesters of tuition on the off chance we could get him to graduation. So we brought him home at winter break of his Sr year.  At that point we had only one goal. Graduation.  We did not give a shit if he was miserable. Our parent job was for him to do the work to graduate on time.

And he did.

Had my school still been open, I have no doubt SS would have finished successfully.  The school we chose for him was semi-private and did not have the unbreakable environment of zero tolerance that our family tradition school had.

I cannot imagine a parent facilitating what the OP's SD has perpetrated.  Sadly, some kids really do lose the parent lottery.

I make no secret that I won both the parental Power Ball and parental Mega Millions Loto on the day of my birth.

Sadly, OP's SD did not. At least with the BM. Hopefully the Court actually makes a wise decision, SD graduates with a token diploma, and OP and her DH get out of the funding of BM's life.  Unfortunately, then comes the emotionally hard part. When SD crashes and burns in epic fashion.