Does giving in to demands make tantrums worse?

It's true that granting a demand during a tantrum makes it easier to learn "crying gets results." But rather than "never respond," a combination works better: (1) when calm, teach and routinely respond to ways of asking (words, cards); (2) during the tantrum, keep them safe and wait matter-of-factly, responding once they've calmed down. When the request itself is reasonable, it's fine to grant it after they calm down. What matters is having them experience "telling me works," not "crying works." If frequency or intensity is high, consult a professional.