When you say your teachers haven't mentioned other resistance groups, you mean resistance groups within modern day Germany/Austria or Resistance group in general, pertaining all of occupied Europe? That would be pretty strange in both cases.

Maybe the fact that the White Rose is the less controversial and the more appealing to the modern day world?

[LONGER ANSWER]

Let's take the most famous act of Resistance inside Germany: the von Stauffenberg coup (Operation Valkyrie) is surely more controversial than the White Rose when taken at closer scrutiny. Hollywood made those officers pass as martyrs and saints, but it could be argued that it wasn't really the case. A good portion of them were nationalist conservatives (and NOT democratics) that wanted Hitler removed to try some negotiation with the western allies - to stop the inevitable soviet invasion. Most of them weren't that unhappy as long as Hitler was victorious, and profited from nazism until things started to go for the worse. Stauffenberg himself was pretty enthusiast of the German colonization of Poland.

And outside of Germany: more often than not the so called "Resistance" was formed by various groups with different goals. For example, under the CLN (National Resistance Committee) in Italy we had monarchists, republicans, democrats, christians democrats, socialists, communists, liberals and social-liberals.

So, a large portion of Resistance groups in France, Italy, Yugoslavia and of course the URSS was formed by communists. Since ever more often communism and fascism are compared as being the same thing (I'd argue it's false, but whatever you believe), maybe it gets harder to talk about communist resistance. Other groups, like the Armia Krajowa in Poland, were instead fiercely nationalist. I think that most of those groups (I can talk about Italy and Yugoslavia for experience) have some controversy attached somehow. The italian resistance is often accused of...resisting, as if the german reprisals were totally ok and lawful, and it was italian resistance fault, not nazi Germany's. Then there are the reprisals the resistance groups would had committed themselves after the war/liberation. It's a pretty heathed debate, too long to be further discussed here. I suspect each european country has similar debates.

Even if it's not about WWII, but decolonization, you should watch the 1966 movie "The Battle of Algeri". That movie is pretty honest about what guerrilla warfare and resistance is about...

Anyway!

[LONGER ANSWER/over]

Let's just say that compared to those (arguably) hypocrite aristocrats, nationalists, communists etc., with all the attached controversies and discussions, a small group of democratic and catholic german youth, risking (and eventually losing) their heads in non-violent actions against their own country's regime looks much better for today's standard than guerilla warfare, assassinations, bombings etc.

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[POST SCRIPTUM]

That said, I wouldn't judge the valor of a Resistance groups only by the results they managed to achieve. Just think about the efforts of doomed Armija Krajowa in Warsaw. They tried to uprise to free the capital city by themselves, thinking that the soviets would have been there in a short time and the germans would have retreated, as often happened...but the soviets just stopped outside of Warsaw. Was it because they wanted to have those polish nationalists killed by germans? Or was it because they were at the end of a gigantic and costly offensive, with shortages of fuel and fatigue? Either way, the Armia Krajowa was defeated after a bitter two-months battle, which saw terrifying war crimes committed against the civilian population and Warsaw completely destroyed. Well, did this had some impact on the war or on Poland destiny? Sadly for them, no, not really.

The White Rose's students did what only a very few people had the courage (or interest) to do in 1942 Germany. I think it's an important example, still worth talking about today.

Sure, if your teachers haven't mentioned ANY other resistance groups, inside or outside Germany, well, I'd say they did your class a disservice...