D.B.
A lot depends on what kinds of warnings he, and you, had all year. Were you both given progress reports? Were you both aware of the consequences of continued failing grades and failure to turn in work? Was summer school discussed as a way to make up missed work and lessons? It's not just about testing - it's about handling the responsibilities of 8th grade. If he cannot handle those, he's not ready for the rigorous standards of high school.
Does he have a learning disability of some kind? Do you have an IEP? Does he need extra supports in some areas? Were those discussed, selected, implemented?
Or did your son know that there was a risk of not passing, and he ignored that? What consequences did he have all year long (from you, from the school) for failing to do his work? Did you make excuses for him? Do you have the ability to help him with his work, or should you have gotten him a tutor or some help through the guidance office? Usually there isn't just one person at fault in these situations - usually it's shared responsibility.
I would consider taking your son to the meeting. Start with the idea that everyone wants your son to succeed - he wants to succeed, you want him to, the school wants him to. But everyone - EVERYONE - has a job here and it only works if you all understand your role and don't just place blame on others.
Holding back is a wait for your son to have a "do-over" rather than go to high school with even more responsibility and fail at that. It's okay for him to learn the hard way that decisions have repercussions. He cannot continue to turn in work late and think that the school doesn't mean it that this is a requirement for passing. Hard lessons, yes. But sometimes kids have to be inconvenienced. High schools, colleges, and employers don't tolerate and excuse laziness and forgetfulness. Better that your son learn this now, buckle down with his studies, and stop doing whatever distracts him (computer, video games, friends, texting, whatever). Your job is to help him do what is necessary, not what he thinks he wants now. Sometimes that means making unpopular decisions but it's a good life lesson.