No, danios will not school with guppies. Danios will only school with their fellow danios, so you can’t expect them to school with guppies or any other fish. To prevent your danios from getting stressed or lonely, keep at least five of them together so that they can form a school.
However, that doesn’t mean you shouldn’t keep danios and guppies together. Danios and guppies are compatible tank mates, as they’re both are quite peaceful and have similar environmental requirements.
Make sure not to overcrowd the tank. As a general rule, one inch of fish requires one gallon of water. Full-grown danios and guppies are typically two inches long, so you’ll need a 15-gallon tank or larger to keep small schools of danios and guppies.