The traditionally state realm of education is an area where non-citizens have enjoyed substantial membership rights. Nyquist v. Mauclet involved a relatively straightforward application of Graham: the plaintiffs were lawful permanent residents challenging a New York state rule that limited higher education funding to citizens, persons intending to become citizens, or refugees. The Supreme Court found that that the rule triggered strict scrutiny and struck it down.
A more difficult question arose in Plyer v. Doe, which concerned the rights of undocumented children to education. The Court stopped short of applying strict scrutiny, acknowledging that the children's unauthorized status merited different treatment from the lawful immigrants in Graham. Instead, it applied a kind of intermediate scrutiny, ultimately finding that Texas's effort to cut off education for unauthorized migrant children was unconstitutional. The Court's finding that Texas's law violated equal protection is probably an outlier, unlikely to be repeated outside the unique context of an important right like education and sympathetic child plaintiffs.