With you. When we switched the oldest to homeschooling, I told the children outright that my goal for them was to score in the 80%s on summative assessments, as an indication that their instruction was both challenging and achievable (aka, in the ZPD). We went through periods of much lower formative assessments, as they also wrestled through learning to study, show work, self-monitor, organize, etc.

One of the beauties of home schooling is that one can decide on one's own grading system. Having used Singapore Math throughout (including in secondary), we also adopted the grading system used in many Singapore classrooms for our math courses, which includes much more challenging problem-solving on assessments, but also sets 80% as the minimum score for an A+. This allows us to have both ZPD and "good" grades.

...pronounced like the long vowel and first letter of the alphabet...