The game if can should be avn, sandbox okay but not much grind are good
You did not say if you have any preferences about what role the MC should have: student or teacher?
MC as student:
Photo Hunt: Ren'Py engine & DAZ renders of high quality. Love Interests are both older women incl ones own mother, and schoolgirls of the same age incl ones sister. Story is sandbox, with multiple paths for different LI's.
Chloe 18: 'other' engine with DAZ(?) renders of decent quality. OBS! MC is the female Chloe, except I think in one of the games. Story is generally based on Chloe being corrupted sexually, and at times reluctantly.
HS Tutor: Renpy + HoneySelect/Illusion. Love Interests are mother and sister, most girls in the class pls their mothers, some teachers in the school. Sandbox.
MC as teacher/headmaster:
The Headmaster: Renpy + HoneySelect or some other Illusion renderer. Love interests are all the schoolgirls plus some adult women. Sandbox with a storyline. Main activity is punishment and corruption of schoolgirls, with spankings and sexual activities. Some reluctance in some girls.
DropOut Saga: Renpy + HoneySelect/Illusion. Love Interests seems to be two adult women and probably all of the schoolgirls. As far as I remember, no sex with the scoolgirls yet(?). Has a mafia backstory too. Still pretty early in the game development though.
Games where the school life is not the major stage of action:
Eternum. Once in a Lifetime. Ripples.
Games I have not really played yet, but seems interesting:
FreshWomen: Renpy and DAZ. Renders of girls seems pretty nice
The Awakening: Renpy and DAZ. I have only played this one a little. Love interests are sister, mother, female classmates, as far as I've seen. Renders are decent to good DAZ.