Does everyday household spending earn reward, rather than being merely a duty?

Yes, and the hadith calls it charity.
The Prophet ﷺ said: when a man spends on his family hoping for reward from Allah, it is charity (ṣadaqah) for him. In another report he said the best charity is that given by one who has means to spare, and begin with those you are responsible for. So school bills and groceries are not “ordinary spending” separate from worship — with the right intention they count as good deeds. See Family finances.