Train the German nouns that add -n or -en outside nominative singular: der Student, den Studenten, dem Studenten, des Studenten. Includes flashcards, case tables, ending drills, sentence practice, error spotting, categories, and spaced review.
Most weak masculine nouns add -n or -en in accusative, dative and genitive singular, and in plural forms. Nominative singular stays unchanged.
Watch masculine nouns ending in unstressed -e, nationalities, people/animals, and many foreign-origin endings such as -ant, -ent, -ist, -oge, -at.
Some nouns like der Name add -ns in genitive singular: des Namens, but dem Namen, den Namen.
After den, dem, des with these nouns, say the noun aloud and check whether the noun itself also changed.