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These are usually Flash (now legacy) or HTML5 games for early elementary grades.
Several indie game sites feature duck characters in math drills, e.g.: duckmath sites
If you’ve come across the term you might be wondering whether it’s a specific platform or a category of educational websites. While no major curriculum or tech company officially uses the name “DuckMath,” the term appears to be emerging in informal contexts—often referring to fun, animal-themed (especially duck-themed) math practice websites, or as a misspelling of existing resources. These are usually Flash (now legacy) or HTML5
If you remember part of the name, a duck character, or a particular math skill (e.g., multiplication, fractions), provide those details, and I can narrow down the search for you. a duck character