This article keeps you on the right track when it comes to learning ways to say in Spanish that something, or someone, fails.
Don't Fail to Take Notice of This Verb!
From failing a course to failing to do something, to disappointing someone... there are a number of uses of to fail in English. Let's explore the various verbs in Spanish that correspond to the many faces of this one English verb.
The Spanish verb fracasar is usually the first one listed in bilingual dictionaries, It doesn't cover as much ground as the English verb. It means to not succeed at something, or to generally make a mess of things in some way.
Miguel, no va a fracasar esta vez (Miguel isn't going to fail this time).
No vayas a fracasar, ¿eh? (Don't go and mess up, ok?)
The same verb can be used to express failing a class, but usually the verb suspender or the verb phrases quedar suspendido or ser suspendido are used when referring to failing a course. Note that the form suspendida as well as the plural forms suspendidos/suspendidas must be used if referring to more than one person or more than one female subject.
Mi amigo fracasó en la clase de geografía (My friend failed the geography class).
Mis amigas quedaron suspendidas el trimestre pasado (My [girl]friends flunked last quarter).
Nunca he sido suspendido (I have never flunked [a class, quiz, etc.]).
The verb suspender can be used actively, that is, when the professor is the subject, to show that he or she flunked someone:
El professor me suspendió (The prof flunked me).
The noun suspenso -- meaning a failing grade -- can be used too (even though the actual word for a grade in Spanish is una nota):
Me dio un suspenso (He gave me a failing grade).
When English speakers mean to fail to do something rather than failing at something, Spanish uses dejar de plus an infinitive:
Mis alumnos dejaron de entregar su trabajo final (My students failed to hand in their final paper).
This same construction, depending on context, also means to quit doing something, such as a bad habit:
Mi abuelo dejó de fumar (My grandfather quit smoking).
To not keep one's word or to break one's promises is expressed with falter a, as well as simply falter and the indirect object pronoun referring to the person who has been deceived, disappointed or otherwise impacted by the subject's turpitude:
Susana siempre falta a su palabra (Susan never keeps her word).
Esa chica me faltó cuando salió con Juan (That girl disappointed/deceived/failed me when she went out with Juan).
Finally, using most any action verb in the preterite with no in front of it will convey the idea of failing to...:
El tren no vino (The train failed to show).
Los perros no encontraron el conejo (The dogs failed to find the rabbit).