One decision that hasn't been mentioned, and makes a perfect entry to constitutionalism and civil rights, is
The Slaughter-House Cases and the denial of the extension of the Privileges or Immunities Clause of the Fourteenth Amendment to the states. This might not be appropriate for the level of a high school class, though. This is a case that future justices, including Thomas and Scalia among them, thought led to an errant extension of both the Due Process and Equal Protection Clauses to the states from the federal bench. It would have, they argued, been jurisprudentially neater to simply have relied on a different interpretation of the P & I Clause to decide the case and subsequent cases that involved the same question. Instead, we got the Lochner Era, The Warren Court, and the use of Substantive Due Process plus the torturous use of the EP Clause to ensure more substantive rights at the state level than those Clauses textually and originally were intended to bear, in some people's opinions.
https://en.wikipedia.org/wiki/Slaughter-House_Cases
I would second
Kelo and
Wickard as the two cases that the Supreme Court got really wrong on all accounts, though the utility of the Interstate Commerce Clause was indeed radically transformed, some would say for the better, by
Wickard.
Wickard is more of a partisan one than
Kelo is, which cut through all political stripes and was received as a terrible decision and frankly, an un-American one.
Plessy is also one, but it was
de facto overruled 9-0 by a policy-based decision in
Brown v. Board Of Education and subsequent cases to it.
Neat fact about
Kelo to me: My former Dean and a near-adjunct prof of mine (I dropped the class) argued that case
for Connecticut at the state level. Both are flaming liberals, if you'll forgive me politics for the moment. The Dean was also my Property professor and used a former students' essentially Marxist casebook to teach property law. Wes Horton was an adjunct prof of appellate law, as well he should have been, winning the two biggest cases at the state level in recent memory.
The Dean tried to sell the case as an example of federalism and allowing state legislatures to govern as they saw fit. Yeah, right...wonder what he thought about
Roe and federalism...just saying. Anyhoo...that's my two cents.