We had the exact same experience. BM claims to be a "good mother" who cares about education, but nearly six years of observation on my part shows otherwise. One SS has never done homework. BM always tried to convince DH that she "had an agreement" with the special ed teacher that SS didn't need to do all the homework, but he still got marked down, so I don't think that was an actual agreement. Anytime BM had a conflict with a teacher or thought the teacher was expecting too much of one SS or the other, she would just go in and cry to the counselor and get them moved to a different class or have the class dropped entirely.

In fifth grade, DH tried to support SSs in doing their homework by calling them every day and working on it over the phone, which usually involved looking at a texted picture of the assignment and working through problems that way. That was the only semester that both SSs consistently turned in homework. BM pitched a fit and said DH was "disrupting" her time. Then enmeshed SS (the one who never does anything) would refuse to talk to DH because he was "going to work on homework with mom" only to call us hours later because BM either couldn't or wouldn't work on it. 

Both kids have IEPs, but they are vague and not likely to meet any needs. The actual needs are also unidentified. I work in education. I am not a special ed expert, but from my limited experience, neither SS is receiving accommodations or supports that will help them, they are just being put in the "resource room" where they seem to stagnate below grade level. When schooling went "remote" in March, both SSs stopped participating at all. There was no excuse, they have internet access and have parents working at home. They didn't even join the session the special ed teacher in middle school set up to connect them with the special ed teacher in high school. I asked them about remote school once and they told me "we don't have to do it. It's all just review." I just said, "I don't think that's true" and left it at that. In the past, I've been accused by BM of "making them feel bad" and even causing OCD in one SS because I've made him feel so anxious about school.

DH did not have a positive school experience himself, so he's largely checked out at this point because it's triggering for him. I, as the stepmother, have also checked out because a) it's triggering for me because working hard and valuing education are two of my values and it's difficult for me to have to deal with children who don't share those values; b) I can't put more care and effort into education for these kids than their parents.

School has started remotely out here. I've looked at SSs schedules and based on their level of competence, their schedules are two difficult for them, but I know BM a) has not looked at the schedules and b) would not be able to assess the difficulty of those schedules even if she had looked at them, so I'm sure if and when they decide to engage in school work, that one or both of them will reshuffle their schedules mid-year. I know BM hasn't logged on because one SS still owes $120 in school fines for last year. Strangely enough, someone added a random amount of money to their food services accounts ($10.67 for one and $10.68 for the other) last week even though school is remote, so neither kid is buying any food at school. 

Our state requires 24 credits to graduate and students at SSs school only take 6 credits per year, so there is no wiggle room for them to fail or drop any classes. My only hope right now is that they graduate on time, because I need DH's legal obligations to BM to end and right now that will happen when they "turn 18 or graduate". They will turn 18 a month before they are scheduled to graduate. 

My brother chose to restart the second half of his Jr. year of HS when he was nearly halfway through his Sr. year of HS.  He changed schools to do it.  At the time he was not particularly motivated accademically but enjoyed football.  He was on the bubble grade wise regarding qualifying to play sports, particularly football.  At that time he was pulled from class one day to meet with a team of academic assessors.  The previous year he had taken the PSAT and had scored the second highest score ever seen in that school district. That a marginal student had scored that high of a score got the significant attention of the district leaders.  The concern was that he had cheated They did a bunch of testing on him and concluded he was entirely capable of that level of PSAT score and was just not a particularly interested student.

At that point he came to the epiphany that he would do himself a favor by making a concerted effort accademically.   He did not have time to recover enough in the last semester of his Sr. year so ... he did a rewind of a year to the mid point of his Jr. year and did great from then until HS graduation a year later than would have been his on schedule graduation date.

I had a do-over of my Sophomore year.  I was an honor student, Jr. National Honor Society, etc... through Jr. High (for the younger crowd, Jr. High was 7-9th grade).  I went off to boarding school for HS.  My first sophomore year was at a Lib Arts boarding school that was not particularly structure. I had way too much of a good time.  My second Sophomore year through HS graduation was at Military school.  I was extremely successful in the structure environment and I have gone on to a notably successful professional career. Not as successful as some but far more successful than most.

We considered delaying SS's start for Kindergarden.  He is a "late summer boy" which apparently are the bane of many teachers when it comes to difficult kids in class.  We discussed it with his preschool teacher who begged us not to hold him back.  She said all he talked about was riding the big kid school bus and going to big kid school. He was extremely advanced in his preschool class though he was the youngest kid in class.  She said if we held him back the risk was that he would be bored for the rest of his school years.  So, we kept him on schedule.  He was an extremely well behaved kid but.. was usually bery bored every school year. The first 6wks of school he was interested and an extremely high performer.  After the first 6wks each year he drove his teachers insane. He would sleep or read novels in class and pretty much ignore the lessons and would not do his homework. He was still impeccably polite and extremely well behaved. He was just totally disengaged and uninterested in the classroom and school work.  

We tried the changing schools thing which worked wonders until the Spermidiot helped SS to hack the school firewall and SS would stay up all night playing WoW with his SpermDad.  So, we brought SS home at winter break, put him in our local HS and gave him only the last semester of HS to graduate on time or he was out.  I took him on a tour of the homeless camp under the Insterstate in Philly to meet his future neighbors.  SS was so petrified that he graduated on time and with honors though he had a year and a half of work to complete in a single semester.  We moved a few weeks after we dropped him off for Military School so when we brought him home to finish HS he was at a school where he knew no one.  That whole experience scared the shit out of him enough to re-engage his brain and extricate his head from his ass so he completed HS successfully.

My brother is now the COO of a prominant international company and my Skid is doing very well in his USAF career.

A shakeup/epiphany inducing moment is a viable tool to use with some kids. It is probably less effective on younger kids than on older kids.

But... it is a thing.